CCNA第四册第一章答案(100分)

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人教版高中英语选择性必修第四册UNIT1 Section Ⅰ 含答案

UNIT 1SCIENCE FICTIONSectionⅠReading and Thinking一、单词拼写1.Although it is a work of (小说),it is based on the stories that happened in the￡1,000 (奖金) for being the best salesperson of the year.(诚实正直) who has never abandoned her principles for the(内疚的) at forgetting about Tom’s birthday.(暂停) for more than 30 days will have to1.In some cases people have had to wait several weeks for an (appoint) for theirin our school to see.No one can easily succeed.all,Rome is not built in one day.the patients.(take) more exercise and have enough sleep to keep(hold),some workers were1.Friendly neighbours are trying to make the community (更像是) a big.Much to our amazement,the five-year-old boy should read,(更准确.(真奇怪) Mary hasn’t(那儿站着一位陌生的男士).Shopping centres,stadiums and universities may soon have a new tool to help fight crime.A California company says its robots can predict and prevent crime.It says the goal is to reduce crime by half in areas the robots guard.The chief executive officer of the company says,“These robot security guards will change the world.Our planet has more than seven billion people on it.It’s going to quickly get to nine billion people.The security equipment that we have globally is just not going to develop that fast.The company’s Autonomous Data Machines can become the eyes and ears of law enforcement(执法).”“You want them to be machines plus humans.Let the machines do the heavy and sometimes dangerous work and let the humans do the strategic decision-making work,so it’s always working all together.”The machines do not carry weapons but they have day and night video cameras which are able to turn 360 degrees and can also sense chemical and biological weapons.Some people may become concerned about their privacy,especially in connection with the video recordings.Some people may worry that such recordings will appear on the Internet.A law professor says the machines have to be used in the right way and it will be interesting to see how state laws deal with this kind of video.The officer says there is a long waiting list for the robots in the US.Workers in the company are working overtime to meet the demands of the market.At least 25 other countries are also interested in these robot security guards.1.What can this new tool do for humans?A.Make strategic decisions.B.Keep watching day and night.C.Carry heavy weapons.,这种机器人能够日夜不停地执勤站岗。

物理光学第四版第一章习题答案

1.28 弯曲的圆柱形光纤，光纤芯和包层的折射率分别为 n1和n2(n1＞n2)，光纤芯的直径为D，曲率半径为R。
证明入射光的最大孔径角2u满足关系式:
D 2 sin u n1 n2 (1 ) 2R
2 2
c u’
sin c sin( u '90 ) cos u ' D D R R R 2 2
5．已知平面波的法线与单位矢量n(，，)平行，试写出该单色平面波的方程。
单色平面波波动方程：
E A cos(t k r )

2 k n

E A cos(t k r ) A cos[t (x y z )]
6 利用波矢量的方向余弦cos，cos，cos。写出平面波的波函数；并证明它是三维波动方程的解。
2E 2 2 k (cos ) E 2 z
2 2
2E 2 E 2 t
2
ky kx kz z
k
Q cos cos cos 1
k E
2
x
2
v2
E
2
2f 2 2 ( ) k v2 f
7 平面光波从A点传播到B点，在AB之间插入透明薄片L＝1mm，折射率n＝1．5。假定光波的波长＝500nm，试计算插入薄片前后B点位相的变化。答：假设A点的初相为零，因此求插入薄片前B点的变化．前：后：
光波以布儒斯特角入射到两介质界面时
1 2
∴

2
且tg1 n
2 cos2 1 2 cos2 1 1 1 tp sin(21 ) 2sin1 cos1 tg1 n
1.21 光束垂直入射到45˚直角棱镜的一个侧面，光束经斜面反射后从第二个侧面透出。若入射光强度为I0,问从棱镜透出光束的强度为多少？设棱镜的折射率为1.52，并且不考虑棱镜的吸收。

新理念外语网络教学平台第四册Unit1测试答案

全新版第二版综合B4U1-APart I Listening Comprehension ( 15 minutes )Section ADirections: In this section, you will hear ten statements. Numbers 1 to 6 are based on Text A while the rest are based on Text B. Each statement will be read ONLY ONCE. Listen carefully and decide whether each statement is true or false.1.A) TB) FScript: When the Grand Army led by Napoleon attacked Russia, the Russians fought bitterly against them.正确答案：B2.A) TB) FScript: The battle at Smolensk was a decisive victory for Napoleon.正确答案：B3.A) TB) FScript: The Russian czar refused Napoleon’s truce offer because he knew that the severe Russian winter would defeat Nap oleon’s army.正确答案：A4.A) TB) FScript: Napoleon ordered his Grand Army to retreat from Moscow only because the weather there was too cold.正确答案：B5.A) TB) FScript: Hitler expected to conquer the Soviet Union in five weeks.正确答案：B6.A) TB) FScript: In answer to the call of the “scorch the earth” by Stalin, the Russians burned or destroyed their farms and factories.正确答案：A7.A) TB) FScript: In order to open up a second front in Europe, British, American and Canadian forces did a lot of careful preparations for more than a year.正确答案：A8.A) TB) FScript: The days of 5, 6 and 7 June were chosen for D-Day because moonlight and tide of these days were favorable to landing.正确答案：A9.A) TB) FScript: When the assault on Normandy began on the midnight of 6 June, the German troops were on high alert.正确答案：B10.A) TB) FScript: Thanks to a southerly current, the landing at the new sector of Utah Beach was quite正确答案：ASection BDirections: In this section, you will hear a passage three times. When the passage is read for the first time, you should listen carefully for its general idea. When the passage is read for the second time, you are required to fill in the blanks with the exact words you have just heard. Finally, when the passage is read for the third time, you should check what you have written.The Winter War was a military conflict between the Soviet Union and Finland. It began with a Soviet (11)_________________ on 30 November 1939 and ended on 13 March 1940 with the Moscow Peace (12)_________________ . The League of Nations deemed the attack (13)_________________ and expelled the Soviet Union from the League on 14 December 1939.The Soviet forces had three times as many soldiers as the Finns, 30 times as many aircraft, and a hundred times as many tanks. The Red Army, however, had been (14)_________________ by Soviet leader Joseph Stalin’s Great Purge of 1937, reducing the army’s (15)_________________ and efficiency shortly before the outbreak of the fighting. With more than 30,000 of its army officers (16)_________________ or imprisoned, including most of those of the highest ranks, the Red Army in 1939 had many (17)_________________ senior officers. Because of these factors, and (18)_________________ and morale in the Finnish forces, Finland was able to resist the Soviet invasion for far longer than the Soviets expected.Hostilities ceased in March 1940 with the signing of the Moscow Peace Treaty. Finland ceded 11% of its pre-war territory and 30% of its economic assets to the Soviet Union. Soviet losses on the front were heavy, and the country’s (19)_________________ . The Soviet forces did not accomplish their objective of the total conquest of Finland, but did (20)_________________ along Lake Ladoga to provide a buffer for Leningrad. The Finns, however, retained their sovereignty and enhanced their international reputation.Script: The Winter War was a military conflict between the Soviet Union and Finland. It began with a Soviet offensive on 30 November 1939 and ended on 13 March 1940 with the Moscow Peace Treaty. The League of Nations deemed the attack illegal and expelled the Soviet Union from the League on 14 December 1939.The Soviet forces had three times as many soldiers as the Finns, 30 times as many aircraft, and a hundred times as many tanks. The Red Army, however, had been crippled by Soviet leader Joseph Stalin’s Great Purge of 1937, reducing the army’s morale and efficiency shortly before the outbreak of the fighting. With more than 30,000 of its army officers executed or imprisoned, including most of those of the highest ranks, the Red Army in 1939 had many inexperienced senior officers. Because of these factors, and high commitment and morale in the Finnish forces, Finland was able to resist the Soviet invasion for far longer than the SovietsHostilities ceased in March 1940 with the signing of the Moscow Peace Treaty. Finland ceded 11% of its pre-war territory and 30% of its economic assets to the Soviet Union. Soviet losses on the front were heavy, and the country’s international reputation suffered. The Soviet forces did not accomplish their objective of the total conquest of Finland, but did gain sufficient territory along Lake Ladoga to provide a buffer for Leningrad. The Finns, however, retained their sovereignty and enhanced their international reputation.正确答案：offensive正确答案：Treaty正确答案：illegal正确答案：crippled正确答案：morale正确答案：executed正确答案：inexperienced正确答案：high commitment正确答案：international reputation suffered正确答案：gain sufficient territoryPart II Reading Comprehension ( 25 minutes )Section ADirections: In this section, there is a passage with several blanks. You are required to select one word for each blank from a list of choices given in a word bank following the passage. Read the passage through carefully before making your choices. Each choice in the bank is identified by a letter. You may not use any of the words in the bank more than once.As Hitler’s armies drew closer and closer to Moscow, an early, severe winter 21 the Soviet Union, the harshest in years. Temperatures dropped to minus 48 degrees Celsius.Heavy snows fell. The German soldiers, completely 22 for the Russian winter, froze in their light summer 23 . The German tanks lay 24 in the heavy snowbanks. The Russian winter brought the German offensive 25 .By the summer of 1942, Hitler had launched two new 26 . In the south, the Germans captured Sevastopol. Hitler then pushed east to Stalingrad, a great industrial city that stretched for 48 kilometers along the Volga River. Despite great suffering, Soviet defenders refused to 27 Stalingrad.In November 1942, the Russians launched a 28 . With little or no shelter from the winter cold in and around Stalingrad, German troops were further weakened by a lack of food and supplies. Not until January 1943 did the Germans give up their siege. Of the three hundred thousand Germans attacking Stalingrad, only ninety thousand 29 soldiers were left. The loss of the battle for Stalingrad finally 30 against Hitler. The German victories were over, thanks in part to the Russian winter.A) uniforms B) settled over C) to a halt D) counterattackE) unprepared F) siege G) buried H) give upI) offensives J) dropped K) captured L) thanksM) turned the tide N) shelter O) starving21. ______________________正确答案：B22. ______________________正确答案：E23. ______________________正确答案：A24. ______________________正确答案：G25. ______________________正确答案：C26. ______________________正确答案：I27. ______________________正确答案：H28. ______________________正确答案：D29. ______________________正确答案：O30. ______________________正确答案：MSection BDirections: There are several passages in this section. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A), B), C) and D). You should decide on the best choice.Passage OneQuestions 31 to 35 are based on the following passage.Terrorism may be viewed as the use of force or violence against persons or property to threaten or coerce (迫使) a government, a formal organization, or a civilian population for political, religious, or social objectives. Since terrorists commonly use violence against civilian targets, their actions are widely condemned as morally unacceptable. In practice, as with a great many other behaviors, what constitutes terrorism is a matter of social definition. When nations resort to violence to further their interests, the results are considered as being legal warfare. In many respects, terrorism is an extension of that approach by people who lack the armies of a state.For many years the public, government officials, and scholars treated terrorism primarily as a "nuisance." But recently, we have come to see terrorism as a new mode of warfare with far-reaching implications. Terrorism serves as an avenue of political expression for some militants (好战分子), whether they are motivated by ideology, ethnicity, or religion. However, what distinguishes much contemporary terrorism is not so much its motivation or purpose, but rather the extent of state involvement in carrying out well-planned and highly destructive acts against adversary nations.Another feature of contemporary terrorism has been the extent to which it has become a media event. Terrorism is usually aimed at a media audience, not the actual victims. The act of media coverage also enhances the importance of "the problem" that led to theterrorist activities. Newspaper readers and television viewers see "the problem" as of much greater importance and as justifying national or international action.31.According to the passage, terrorism is widely unacceptable ______.A) for its illegal actionsB) because it is often targeted at ordinary peopleC) as it usually leads to death and hatredD) for its violence正确答案：B32.The word "approach" at the end of the first paragraph refers to ______.A) legal warfareB) establishing a stateC) furthering one's interests via violenceD) terrorism正确答案：A33.People used to ______.A) underestimate the influence of terrorismB) pay much attention to terrorismC) suffer less from terrorists' actionsD) have sympathy with the terrorists正确答案：A34.Terrorism in the past ______.A) had different objectivesB) had different motivationsC) was more influentialD) was less closely related to governments正确答案：D35.Terrorists use media mainly ______.A) to make their aim known to the worldB) to carry out violent actionsC) as an avenue of political expressionD) to condemn the adversary nations正确答案：APassage TwoQuestions 36 to 40 are based on the following passage.As traditionally grown, under a canopy (株冠) of shade trees and amid other vegetation, coffee is an environmentally-friendly crop. The shade trees fix nitrogen in the soil, fostering the growth of the coffee bushes, and their fallen leaves provide nutrients, further reducing the need for chemical fertilizers. The mixture of vegetation prevents erosion and protects the coffee from harsh weather. In contrast to corn and cattle, which almost always require clear-cutting, coffee can be grown in relative harmony with the rain forest.Recently, however, many coffee farmers in northern Latin America have reduced or eliminated shade to grow new high-yielding coffee plants under direct sun. Fear of a disease known as coffee leaf rust sparked an early round of conversions, most of which took place in the 1970s. To prevent the spread of the disease, coffee farmers "technified," replacing older, shade-loving coffee varieties, with new varieties, packed in tight hedgerows, that can survive open sun — but only with chemical inputs.Coffee leaf rust never turned out to be a major problem for Latin America. To boost farmers' incomes, the U.S. Agency for International Development (USAID) spent some $80 million from the 1970s to the early 1990s, according to a report (1996) from the Smithsonian Migratory Bird Center and the Natural Resources Defense Council, to help growers in Central America and the Caribbean technify. In countries where USAID was not involved, national coffee federations promoted the change, supporting the technification of 69 percent of Colombia's coffee and nearly 40 percent of Costa Rica's.36.Growing coffee plants under shade ______.A) helps them absorb oxygen from the soilB) provides nutrients for other treesC) reduces the need for chemical fertilizersD) creates a mixture of vegetation正确答案：C37.Coffee can be grown amid the rain forest because ______.A) it can stand harsh weatherB) it can be grown together with other plantsC) it doesn't need any chemical fertilizerD) it will not erode in the forest正确答案：B38.Many coffee farmers shifted to growing coffee plants under direct sun in the 1970s ______.A) out of the fear of the spread of coffee leaf rustB) because it was more profitableC) as new varieties of coffee plants were developedD) to decrease chemical inputs正确答案：A39.Coffee leaf rust ______.A) was a great hit to the coffee industryB) cannot be eliminated by chemical fertilizersC) didn't constitute a big problem for Latin AmericaD) ended the growing history of shade coffee正确答案：C40.Many coffee farmers turned to sun coffee ______.A) as a result of the widespread of coffee leaf rustB) because it brought about higher profitC) at the request of USAIDD) with the development of technology正确答案：BPart III Vocabulary and Structure ( 10 minutes )Directions: There are a number of incomplete sentences in this part. For each sentence there are four choices marked A), B), C) and D). Choose the ONE that best completes the sentence.41.They are currently _________ in lengthy trade negotiations.A) engagedB) busyC) obligedD) occupied正确答案：A42.At the first _______ of twelve all the workers in the factory stopped for lunch.A) strikeB) bellC) strokeD) hit正确答案：C43.A solar day is the length of time _______ the Earth to revolve once around the Sun.A) takesB) takes itC) it takesD) one takes正确答案：C44.He obviously displays a great ______ for some of your poems.A) consentB) admirationC) respectD) pleasure正确答案：B45.The teachers ______ themselves with planning out the work of the coming semester.A) employedB) involvedC) occupiedD) engaged正确答案：C46.I prefer to be a _____ because I don't like to operate.A) doctorB) surgeonC) physicianD) specialist正确答案：C47.The _____ of tests in the United States institutions can be a new and frightening experience for many foreign students.A) frequencyB) presenceC) efficiencyD) confidence正确答案：A48.As it had not rained for several months, there was a _____ of water.A) wasteB) dropC) lossD) shortage正确答案：D49.Despite their good service, most inns are less costly than hotels of _____ standards.A) equivalentB) alikeC) uniformD) likely正确答案：A50.The mechanic said that the work would be done quickly, but he would not _____ himself to a specific time.A) admitC) commitD) submit正确答案：C51.The war may _____, but victory is sure to belong to the peace-loving people.A) drag outB) drag onC) drag upD) drag along正确答案：B52._______ to the Independent War, the United States was an English colony.A) BeforeB) PriorC) FollowingD) Preceding正确答案：B53.She continued to type as fast as ever, though her thumb was badly swollen ______ a hurt.A) inB) forC) withD) from正确答案：D54.She looks to be ______ 40, but as a matter of fact, she is 50.A) older thanB) in the neighbourhood ofC) at age ofD) approximately about正确答案：B55.The crust of the Earth was thin here, and other conditions appeared ______ for drilling.B) imaginableC) curableD) durable正确答案：A56.The Russians were attacked and forced to _____.A) advanceB) retireC) retreatD) draw正确答案：C57.Tom _____ off the field with a foot injury.A) limpedB) limbedC) limnedD) lambed正确答案：A58.The new ________ was put into operation early in 1939.A) tacticB) tactC) toxicD) tract正确答案：A59.Britain made a(n)______ of war on Germany in 1914.A) announcementB) statementC) claimD) declaration正确答案：D60.You mustn’t lose heart, sooner or later your effort will pay ______.A) forB) outC) offD) up正确答案：CPart IV Translation ( 10 minutes )Directions: Complete the sentences by translating into English the Chinese given in brackets.61. Everyone knows ____________________ (做到劳逸结合的重要性).正确答案：the importance of striking a proper balance between work and rest62. ____________________ (政府已决定整治城市犯罪) so that a daylight bank robbery will no longer happen.正确答案：The government has decided to clean up the city63. On many issues ____________________ (约翰和玛丽发现他们意见严重分歧).正确答案：John and Mary found themselves seriously at odds64. It was an uneasy night and ____________________ (那婴儿不停地抓弄床罩).正确答案：the baby kept picking at the coverlet65. The little girl was ____________________ (非常迫切地想知道) what her parents brought her as birthday present.正确答案：dying to see全新版第二版综合B4U1-BPart I Listening Comprehension ( 14 minutes )Section ADirections: In this section, you will hear ten statements. Numbers 1 to 6 are based on Text Awhile the rest are based on Text B. Each statement will be read ONLY ONCE. Listen carefully and decide whether each statement is true or false.1.A) TB) FScript: Both Napoleon and Hitler failed in their invasion of Russia because of the raw, bitter, bleak Russian winter.正确答案：A2.A) TB) FScript: In invasion of Russia, Napoleon led a well-trained and well-equipped army, and used “lightning war” tactics.正确答案：B3.A) TB) FScript: In the face of Napoleon’s ass ault, the Russians retreated eastward without resistance.正确答案：A4.A) TB) FScript: After Napoleon captured the capital of Russia, he was very happy because French army could get a lot of treasure there.正确答案：B5.A) TB) FScript: When Napoleon’s Grand Army attacked Moscow, the Russians launched hit-and-run attacks on the French from fields and forests.正确答案：B6.A) TB) FScript: At the Berezina River, Napole on’s Grand Army failed to escape because the Russians burnt the bridges over the swollen river.正确答案：B7.A) TB) FScript: The purpose of the Normandy Landings was only to free French people from the occupation of German army.正确答案：B8.A) TB) FScript: Although the weather of 5 June was bad, General Eisenhower gave the order of the invasion of Normandy.正确答案：B9.A) TB) FScript: At the beginning of the assault, the German army were taken completely by surprise only because of the bad weather.正确答案：B10.A) TB) FScript: The Allied forces led by General Eisenhower succeeded in the Normandy Landings after overcoming many difficulties caused by bad weather.正确答案：ASection BDirections: In this section, you will hear a passage three times. When the passage is read forthe first time, you should listen carefully for its general idea. When the passage is read for the second time, you are required to fill in the blanks with the exact words you have just heard. Finally, when the passage is read for the third time, you should check what you have written.Japan’s attack on Pearl Harbor in December 1941 was one of the most successful surprise attacks in the history of modern (11)_________________ . Japanese warships, including several aircraft carriers, crossed the western Pacific to Hawaii without being seen. They launched their warplanes on Sunday morning to attack the huge American (12)_________________ and air base.Many of the American sailors were asleep or at (13)_________________ . They were completely surprised. In fact, some Americans outside the base thought the Japanese planes must be American airmen making training (14)_________________ in new airplanes. The sounds of guns and (15)_________________ soon showed how wrong they were.The Japanese planes (16)_________________ or seriously damaged six powerful American battleships in just a few minutes. They killed more than three thousand (17)_________________ . They destroyed or damaged half the American airplanes in Hawaii.American forces were so surprised that they were (18)_________________ much of a fight. Japanese losses were very light.Japan’s destruction at Pearl Harbor was so complete that officials in Washington did not tell the full details immediately to the American people. They were afraid the nation might panic if it learned the truth about the loss of so much (19)_________________ .The following day, President Roosevelt went to the Capitol building to ask Congress for a declaration of war against Japan. The Senate (20)_________________ without opposition. In the House of Representatives, only one congressman objected.Three days later, Germany and Italy declared war on the United States. Congress reacted by declaring war on those two countries.Script: Japan’s attack on Pearl Harbor in December 1941 was one of the most successful surprise attacks in the history of modern warfare. Japanese warships, including several aircraft carriers, crossed the western Pacific to Hawaii without being seen. They launched their warplanes on Sunday morning to attack the huge American naval and air base.Many of the American sailors were asleep or at church. They were completely surprised. In fact, some Americans outside the base thought the Japanese planes must be American airmen making training flights in new airplanes. The sounds of guns and bombs soon showed how wrong they were.The Japanese planes sank or seriously damaged six powerful American battleships in just a few minutes. They killed more than three thousand sailors. They destroyed or damaged half the American airplanes in Hawaii.American forces were so surprised that they were unable to offer much of a fight. Japanese losses were very light.Japan’s destruction at Pearl Harbor was so complete that officials in Washi ngton did not tell the full details immediately to the American people. They were afraid the nation might panic if it learned the truth about the loss of so much American military power.The following day, President Roosevelt went to the Capitol building to ask Congress for a declaration of war against Japan. The Senate approved his request without opposition. In the House of Representatives, only one congressman objected.Three days later, Germany and Italy declared war on the United States. Congress reacted by declaring war on those two countries.正确答案：warfare正确答案：naval正确答案：church正确答案：flights正确答案：bombs正确答案：sank正确答案：sailors正确答案：unable to offer正确答案：American military power正确答案：approved his requestPart II Reading Comprehension ( 25 minutes )Section ADirections: In this section, there is a passage with several blanks. You are required to select one word for each blank from a list of choices given in a word bank following the passage. Read the passage through carefully before making your choices. Each choice in the bank is identified by a letter. You may not use any of the words in the bank more than once.Napoleon soon realized he could not feed, clothe, and quarter his army in Moscow during the winter. In October 1812, he ordered his Grand Army to 21 from Moscow.The French retreat turned into a 22 . From fields and forests, the Russians launched 23 attacks on the French. A short distance from Moscow, the temperature hadalready dropped to minus 4 degrees Celsius. On November 3, the winter’s first snow came. 24 horses fell dead in their tracks. Cannon became 25 in the snow. Equipment had to be burned for fuel. Soldiers took ill and froze to death. The French soldiers 26 , leaving the dead along every mile.As the Russian army was gathering its strength, the French had to flee Russia to avoid certain defeat. At the Berezina River, the Russians nearly 27 the retreating French by burning the bridges over the swollen river. But Napoleon, by a 28 of luck, was able to build two new bridges. Thousands of French soldiers escaped, but 29 of fifty thousand dead. Once across the Berezina, the tattered survivors 30 toward Vilna.A) equipment B) Exhausted C) Tiring D) dragged onE) retreat F) hit-and-run G) nightmare H) trappedI) flee J) at the cost K) strength L) limpedM) stroke N) stuck O) escaped21. ______________________正确答案：E22. ______________________正确答案：G23. ______________________正确答案：F24. ______________________正确答案：B25. ______________________正确答案：N26. ______________________正确答案：D27. ______________________正确答案：H28. ______________________正确答案：M29. ______________________正确答案：J30. ______________________正确答案：LSection BDirections: There are several passages in this section. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A), B), C) and D). You should decide on the best choice.Passage OneQuestions 31 to 35 are based on the following passage.We are all inclined to believe that our generation is more civilized than the generation that preceded ours. From time to time, there is even some substantial evidence that we hold in higher regard such civilized attributes as compassion, pity, remorse (懊悔), intelligence and a respect for the customs of people different from ourselves.Why war then?Some pessimistic historians think the whole society of man runs in cycles and that one of the phases is war. The optimists, on the other hand, think war is not like an eclipse (日食) or a flood or a spell of bad weather. They believe that it is more like a disease for which a cure could be found if the causes were known.Because war is the ultimate drama of life and death stories and pictures of it are more interesting than those about peace. This is so true that all of us, and perhaps those of us in television more than most, are often caught up in the action of war to the exclusion of the ideas of it.If it is true, as we would like to think it is, that our age is more civilized than ages past, we must all agree that it’s very strange that in the twentieth century, our century, we have killed more than 70 million of our fellowmen on purpose, at war. It is very strange that since 1900 more men have killed more other men than in any other seventy years in history.Probably the reason we are able to do both, that is, believe on the one hand that we are more civilized and on the other hand wage war to kill ― is that killing is not so personal an affair as it once was. The enemy is invisible. One man doesn’t look another in the eye and run him through with a sword. The enemy dead or alive is largely unseen. He is killed by remote control: a loud noise, a distant puff of smoke and then silence.The pictures of the victim’s wife and children, which he carries in his breast pocket, are destroyed with him. He is not heard to cry out. The question of compassion or pity or remorse does not enter into it. The enemy is not a man; he is a statistic. It is true, too, that more people are being killed at war now than previously because we’re better at doing it than we used to be. One man with one modern weapon can kill thousands.31.In modern wars more people get killed because _____.A) people are more cruelB) people don’t care others’ livesC) people have more advanced weaponsD) people are more civilized正确答案：C32.In what way are we more civilized than the ancients?A) We can kill more people.B) We respect those people different from us.C) We have more interesting stories of war.D) We don’t think of killing as a personal affair anymore.正确答案：B33.In modern war the enemy is treated as _____.A) an animalB) a victimC) a manD) a statistic without life正确答案：D34.How is the enemy killed in modern war?A) By an opponent running him through with a sword.B) By a man who knows him well.C) By remote control.D) By a puff of smoke.正确答案：C。

CCNA第四学期官方章节考试题之第四学期《Final_Examination》(附答案)

公司与AA2SSH存在不正确的访问控制列表条目。

访问列表中的必须在会防止以明文传输登录信息如果身份验证失败，则会断开PPP 会话连接会发起双向握手容易遭受回送攻击4命令show frame-relay map的输出如下：Serial 0 (up): ip 192.168.151.4 dlci 122, dynamic, broadcast, status defined, active 下列哪三种说法正确描述了所示内容的意义？（选择三项。

）192.168.151.4代表远程路由器的IP 地址192.168.151.4代表本地串行接口的IP 地址DLCI 122代表远程串行接口DLCI 122代表用于连接远程地址的本地编号broadcast表示动态路由协议（例如RIP v1）可通过此PVC 发送数据包active表明ARP 进程正在工作5路由器的SDM 主页会显示哪三点信息？（选择三项。

）ARP 缓存闪存的总容量和可用容量路由表已配置的LAN 接口的数量是否配置了DHCP 服务器该LAN 中路由器的数量6从非军事区分界点本地环路网云确保在确认确保路由器上有通向下列哪三种说法正确描述了CSU/DSU调制解调器用于端接本地数字环路。

CSU/DSU调制解调器用于端接本地模拟环路。

路由器通常被视为路由器通常被视为10在链路质量测试完毕后，路由器在协商第LCPNCP它会被丢弃。

它会被放到队列中，直到主机它会被转换，源端口号保持为它会被分配其端口范围内的第一个可用端口号。

交换虚电路的相关信息将DLCI 映射到网络地址提供流量控制提供错误通知提供拥塞通知发送keepalive 数据包以检验PVC 的工作情况14请参见图示。

下列说法中哪三项正确？（选择三项。

）启用了NAT 过载。

启用了动态NAT。

地址转换会失败。

接口配置不正确。

地址为192.168.1.255 的主机将被转换。

进入0/0/2 接口的流量先被转换，然后才流出串行接口0/0/0。

CCNA第1章考试答案

•试题反馈报告Introduction to Networks (版本6.00) - ITN 第1 章考试以下是针对您未获得满分的试题给出的反馈。

某些交互式试题可能不显示您的答案。

分项分数：1某公司正在考虑是使用客户端/服务器还是对等网络。

下列哪三项是对等网络的特征？（选择三项。

）正确响应您的响应易于创建同时充当客户端和服务器时设备性能更好可扩展安全性提升缺少集中管理实施成本更少由于不需要使用网络设备和专用服务器，对等网络易于创建，复杂性更低，且成本更少。

而且对等网络也没有集中管理。

这种网络安全性更低，不可扩展，而且那些同时充当客户端和服务器的设备可能性能更差。

此试题参考以下领域的内容：Introduction to Networks• 1.1.2 提供网络资源2哪种设备的功能是确定消息在网际网络中传输的路径？正确响应您的响应路由器防火墙Web 服务器DSL 调制解调器路由器用于确定消息在网络中的传输路径。

防火墙用于过滤传入和传出的流量。

DSL 调制解调器用于为家庭或组织提供Internet 连接。

此试题参考以下领域的内容：Introduction to Networks• 1.2.1 网络组件3哪两个条件有助于您从各种网络介质当中选择一种网络介质？（请选择两项。

）正确响应您的响应网络上使用的终端设备的成本所选介质可以成功传送信号的距离需要优先处理的数据类型安装在网络中的中间设备的数量要安装所选介质的环境选择网络介质的条件包括：所选介质可以成功传送信号的距离、要安装所选介质的环境、必须传输的数据量和速度以及介质和安装的成本。

此试题参考以下领域的内容：Introduction to Networks• 1.2.1 网络组件4下列哪两项描述了中间设备？（选择两项。

）正确响应您的响应中间设备可以引导数据路径。

中间设备可以生成数据内容。

中间设备可以启动封装过程。

中间设备可以更改数据内容。

中间设备可以将单个主机连接到网络中。

新版新视野大学英语读写教程第四册unit1答案

新版新视野大学英语读写教程第四册unit1答案Unit 1III.1. idle2. justify3. discount4. distinct5. minute6.accused7. object8. contaminate9. sustain 10. worshipIV.1. accusing... of2. end up3. came upon4. at her worst5. pay for6. run a risk of7. participate in8. other than9. object to/objected10. at bestV1. K2. G3. C4. E5. N6.O7.I8. L9. A 10. DCollocationVI.1. delay2. pain3. hardship4. suffering5. fever6. defeat7. poverty8. treatment9. noise 10. agonyWord buildingVII.1. justify2. glorify3. exemplifies4. classified5. purified6. intensify7. identify8. terrifiedVIII.1. bravery2. jewelry3. delivery4. machinery5. robbery6. nursery7. scenery8. discoverySentence StructureIX.1. other than for funerals and weddings2. other than to live an independent life3. other than that they appealed to his eye . . `4. but other than that, he'll eat just about everything .5. other than that it's somewhere in the town centerX.1. shouldn't have been to the cinema last night2. would have; told him the answer3. they needn't have gone at all4. must have had too much work to do5. might have been injured seriouslyTranslationXI. -1. The plant does not grow well in soils other than the one in whichit has been developed.2. Research findings show that we spend about two hours dreaming every night, no matter what wemay have done during the day.3.Some people tend to justify their failure by blaming others for not trying their best.4.We remain tree to our commitment: Whatever we promised to do; we would do it.5.Even Beethoven's father discounted the possibility that his sonwould one day become the greatest musician in the world. The same istrue of Edison, who seemed to his teacher to be quite dull.6. They were accused by authorities of threatening the state security.XII.l.出入除自己家以外的任何场所时，如果你带有宠物，一定要了解有关宠物的规定。

思科CCNA考试答案(全)

CCNA思科考试答案（全）第 1 章考试1一家拥有10 名员工的小型公司使用单个LAN 在计算机之间共享信息。

哪种类型连接适合此公司？由当地电话服务提供商提供的拨号连接能够使公司方便且安全地连接员工的虚拟专用网络通过当地服务提供商建立的私有专用线路通过当地服务提供商提供的宽带服务（如DSL）答案：4解析：对于这种小型办公室，比较适合通过被称为数字用户线路(DSL) 的常见宽带服务实现Internet 连接，这种服务由当地的电话服务提供商提供。

由于员工人数很少，带宽的问题并不突出。

如果公司较大，在远程站点有分支机构，则专用线路会更加适合。

如果公司员工需要通过Internet 与公司联系，则采用虚拟专用网。

2哪种网络情况需要使用WAN？员工工作站需要获取动态分配的IP 地址。

员工在出差时需要通过VPN 连接到公司电子邮件服务器。

分支机构的员工需要与同一园区网络上的另一座建筑物内的公司总部共享文件。

员工需要访问托管在其建筑物内DMZ 中的公司Web 服务器上的网页。

答案：2解析：当出差的员工需要通过WAN 连接到公司电子邮件服务器时，VPN 将通过WAN 连接在员工笔记本电脑与公司网络之间创建一个安全隧道。

通过DHCP 获取动态IP 地址是LAN 通信的功能。

在企业园区的不同建筑物之间共享文件可通过LAN 基础设施来实现。

DMZ 是企业LAN 基础设施内一个受保护的网络。

3以下哪项描述了WAN 的特征？WAN 和LAN 在同一地理范围内运行，但有串行链路。

WAN 网络归运营商所有。

所有串行链路均被视为WAN 连接。

WAN 可提供到园区主干网的终端用户网络连接。

答案：2解析：WAN 可用于将企业LAN 互连到远程分支机构站点LAN 和远程工作人员站点。

WAN 归运营商所有。

虽然WAN 连接一般通过串行接口实现，但并不是所有串行链路均连接至WAN。

LAN（而非WAN）可在组织中提供终端用户网络连接。

4电路交换WAN 技术的两个常见类型是什么？（请选择两项。

CCNA第四学期官方章节考试题之4.5、《ACL》》（附答案）.doc

1有关下列扩展ACL 的说法中哪两项正确？（选择两项。

）access-list 101 deny tcp 172.16.3.0 0.0.0.255 any eq 20 access-list 101 deny tcp 172.16.3.0 0.0.0.255 any eq 21 access-list 101 permit ip any any拒绝从网络172.16.3.0/24 始发的所有FTP 流量。

会隐含拒绝所有流量。

会拒绝发往网络172.16.3.0/24 的所有FTP 流量。

会拒绝从网络172.16.3.0/24 始发的所有Telnet 流量。

会允许从网络172.16.3.0 始发的 Web 流量。

2如果数据包未与ACL 中的任何语句匹配，则会如何处理该数据包？会将该数据包放置在缓冲区中，并在删除该ACL 后转发该数据包。

会将该数据包连同一则错误通知消息发回给源地址。

列表末尾的隐含permit any语句会允许该数据包通过。

列表末尾的隐含deny any语句会导致该数据包被丢弃。

3请参见图示。

ACL 101 中的"deny ip 64.100.0.0 0.0.7.255 any" 语句发现了 35 个匹配项，最可能的解释是什么？内部网络中的一名用户伪造了一台Internet 主机并正在向该主机发送流量，该主机也正在响应。

Internet 上的一名用户伪造了内部网络中的一个主机地址，并正在尝试向内部网络发送数据包。

一台Internet 主机正在反复要求内部网络发送流量。

内部网络中的一台主机正在反复要求Internet 发送流量。

4标准访问控制列表应该放置在哪里？靠近源地址靠近目的地址在以太网端口上在串行端口上5Cisco 标准ACL 是如何过滤流量的？通过目的UDP 端口通过协议类型通过源IP 地址通过源UDP 端口通过目的IP 地址6ACL 可使用哪三种参数来过滤流量？（选择三项。

计算机操作系统第四版课后习题答案第一章之欧阳索引创编

第一章欧阳索引（2021.02.02）1．设计现代OS的主要目标是什么？答：（1）有效性（2）便利性（3）可扩充性（4）开放性2．OS的作用可表示在哪几个方面？答：（1）OS作为用户与计算机硬件系统之间的接口（2）OS作为计算机系统资源的管理者（3）OS实现了对计算机资源的笼统3．为什么说OS实现了对计算机资源的笼统？答：OS首先在裸机上笼盖一层I/O设备管理软件，实现了对计算机硬件操纵的第一条理抽象；在第一层软件上再笼盖文件管理软件，实现了对硬件资源操纵的第二条理笼统。

OS 通过在计算机硬件上装置多层系统软件，增强了系统功能，隐藏了对硬件操纵的细节，由它们共同实现了对计算机资源的笼统。

4．试说明推劢多道批处理系统形成和収展的主要劢力是什么？答：主要动力来源于四个方面的社会需求与技术成长：（1）不竭提高计算机资源的利用率；（2）便利用户；（3）器件的不竭更新换代；（4）计算机体系结构的不竭成长。

5．何谓脱机I/O和联机I/O？答：脱机I/O 是指事先将装有用户法度和数据的纸带或卡片装入纸带输入机或卡片机，在外围机的控制下，把纸带或卡片上的数据或法度输入到磁带上。

该方法下的输入输出由外围机控制完成，是在脱离主机的情况下进行的。

而联机I/O方法是欧阳索引创编2021.02.02指法度和数据的输入输出都是在主机的直接控制下进行的。

6．试说明推劢分时系统形成和収展的主要劢力是什么？答：推动分时系统形成和成长的主要动力是更好地满足用户的需要。

主要表示在：CPU 的分时使用缩短了作业的平均周转时间；人机交互能力使用户能直接控制自己的作业；主机的共享使多用户能同时使用同一台计算机，自力地处理自己的作业。

7．实现分时系统的关键问题是什么？应如何解决？答：关键问题是当用户在自己的终端上键入命令时，系统应能及时接收并及时处理该命令，在用户能接受的时延内将结果前往给用户。

解决办法：针对及时接收问题，可以在系统中设臵多路卡，使主机能同时接收用户从各个终端上输入的数据；为每个终端配臵缓冲区，暂存用户键入的命令或数据。

计算机网络第四版(课后练习+答案)

第 1 章概述1.假设你已经将你的狗Berníe 训练成可以携带一箱3 盒8mm 的磁带,而不是一小瓶内哇地. (当你的磁盘满了的时候，你可能会认为这是一次紧急事件.)每盒磁带的窑最为7GB 字节；无论你在哪里，狗跑向你的速度是18km/h 。

请问，在什么距离范围内Berníe的数据传输速率会超过一条数据速率为150Mbps的传输线？答：狗能携带21千兆字节或者168千兆位的数据。

18 公里/小时的速度等于0。

005 公里/秒，走过x公里的时间为x / 0.005 = 200x秒，产生的数据传输速度为168/200x Gbps或者840 /x Mbps。

因此，与通信线路相比较，若x<5。

6 公里，狗有更高的速度。

6。

一个客户·服务器系统使用了卫星网络，卫星的高度为40 000km。

在对一个请求进行响应的时候，最佳情形下的延迟是什么?答：由于请求和应答都必须通过卫星,因此传输总路径长度为160,000千米.在空气和真空中的光速为300,000 公里/秒，因此最佳的传播延迟为160,000/300，000秒，约533 msec。

9.在一个集中式的二叉树上，有2n -1 个路出器相互连接起来:每个树节点上都布一个路由器.路由器i 为了与路由器j 进行通信，它要给树的根发送一条消息。

然后树根将消息送下来给j 。

假设所有的路由器对都是等概率出现的,请推导出当n很大时,每条消息的平均跳数的一个近似表达式。

答：这意味着，从路由器到路由器的路径长度相当于路由器到根的两倍。

若在树中，根深度为1，深度为n，从根到第n层需要n—1跳，在该层的路由器为0.50。

从根到n—1 层的路径有router的0。

25和n—2跳步。

因此，路径长度l为：18。

OSI 的哪一层分别处理以下问题？答：把传输的比特流划分为帧--数据链路层决定使用哪条路径通过子网——网络层.28。

一幅图像的分辨率为1024X 768 像素，每个像素用3 字节来表示。

接入网技术第4版课后答案

接入网技术第4版课后答案第一章：网络演进与法规制约一、判断题1、接入网最初的原型是用户环路，仅仅是一种专用设施，附属于电话网甚至附属于特定控交换机。

（∨）2、接入网的竞争给运营商带来了挑战和机遇，同时也给用户带来了更多的选择.。

（∨）3、传统的三网指的是电话网、有线电视网和互联网，随着技术的发展，网络融合是必然趋势。

（∨）二、选择题（说明：本选择题为不定项选择，答案至少有一个。

）1、“最后一公里”可理解为（A ）A: 局端到用户端之间的接入部分B: 局端到用户端之间的距离为1公里C: 数字用户线为1公里D: 数字用户线为1公里2、“fist mile”可理解为（AC ）A: 用户端到局端之间的接入部分B: 用户端到局端之间的距离为一公里C: 对接入网的形象称呼D: 专指数字用户线部分三、填空题1、last mile和first mile都是对__接入网的称呼，表示__核心网和__用户驻地网之间的接入部分。

2、接入网是将用户设备_连接到核心网的网络。

接入网可以只连接一台具体的用户设备，也可以连接由多台用户设备组成的用户驻地网_。

3、AN的英文全称是__ Access Network __，对应的中文名称是__接入网__。

4、现代通信网络的两大基本部件是__核心网__和__接入网__。

5、接入网所具有的__相对独立性和完整性__为用户提供了更多选择的同时，也加剧了网络运营商的竞争。

6、接入网的概念最早是由__英国电信BT __提出的。

7、制定接入网标准的机构是__ ITU-T __。

迄今已制定了两个标准，这两个标准的名称分别是和__ G.902 __和__ Y.1231 __。

四、问答题1、接入网的市场竞争给通信运营商带来了怎样的影响？参考答案：①接入网的市场竞争给通信运营商带来了新的挑战与机会。

②挑战主要体现在：a、争抢用户，满足多业务需求；b、提高服务质量；c、提供新业务；d、发展各种宽带接入技术；e、可能会被淘汰。

ccna1章节与期末答案

第一章：ccna1章节与期末答案正确答案：2.4.5•解析：由于不需要使用网络设备和专用服务器，对等网络易于创建，复杂性更低，且成本更少。

而且对等网络也没有集中管理。

这种网络安全性更低，不可扩展，而且那些同时充当客户端和服务器的设备可能性能更差正确答案：1解析：正确答案： 3.5解析：选择网络介质的条件包括：所选介质可以成功传送信号的距离、要安装所选介质的环境、必须传输的数据量和速度以及介质和安装的成本。

正确答案：3和4解析：终端设备上的应用程序可以生成数据，更改数据内容并且负责启动封装过程。

正确答案：1和4解析：终端设备会发出通过网络传输的数据。

中间设备会在链路发生故障时通过备用路径传输数据，并且会过滤数据传输以增强安全性。

网络介质提供网络消息的传输通道。

正确答案：4解析：外联网是公司外部的人或企业合作伙伴访问数据的网络区域。

内部网只描述通常仅供内部人员访问的网络区域。

当设备连接到有线网络时，有线LAN 会受BYOD（自带设备）影响。

使用大学无线LAN 的设备多为平板电脑和智能手机。

大学生主要使用无线WAN 来访问他们的手机运营商网络。

.正确答案：2解析：由于通过Internet 可以联系在线供应商，所以家庭用户通过Internet 进行网上购物。

内联网基本上是仅供内部使用的局域网。

外联网是外部合作伙伴访问组织内部特定资源的网络。

家庭用户并不一定使用LAN 来访问Internet。

例如，PC 可以通过调制解调器直接连接到ISP。

正确答案：1解析：内部网这个术语用于表示一个组织的私有局域网和广域网连接。

内部网的设计旨在仅允许该组织的成员、员工或其他获得授权的人员进行访问。

正确答案：2和4解析：电缆和DSL 均能实现高带宽、始终联网，并提供到主机计算机或LAN 的以太网连接。

10正确答案：2和3解析：移动电话连接需要使用移动电话网络。

卫星连接通常用于家庭或企业外部不便使用物理布线的位置。

11正确答案：2解析：当对网络资源的请求超出了可用容量时，网络就会变得拥堵。

版本ccna考试第一章期末考试答案b

PDU 封装的正确顺序是什么答案说明最高分值2correctness of response 2 points for Option 10 points for any other option此试题参考以下领域的内容：Introduction to Networks数据封装建立融合网络有何用途为所有终端设备提供高速连接确保平等对待所有类型的数据包实现数据网络基础架构设备的容错能力和高可用性降低部署和维护通信基础设施的成本随着技术的发展，各个公司现在可以将不同的网络整合到一个平台之上，称为融合网络。

在融合网络中，语音、视频和数据通过同一网络传输，从而使人们不必再创建和维护各个单独的网络。

这也降低了提供和维护通信网络基础设施相关的成本。

答案说明最高分值correctness of response 2 points for Option 420 points for any other option此试题参考以下领域的内容：Introduction to Networks融合网络请参见图示。

哪个区域最有可能是图中所示的公司网络的外联网区域A区域B区域C区域D外联网是外部实体访问其他公司的数据的平台。

其形式可能是产品供应商所使用的库存服务器，也可能是外部实体用来访问当天客户数量的当前信息的Web 服务器。

Internet 用云和区域 A 表示。

内部网通常仅供内部人员使用。

区域 B 和 D 均是内部网的示例。

答案说明最高分值correctness of response 2 points for Option 320 points for any other option此试题参考以下领域的内容：Introduction to NetworksInternet主机正在访问远程网络的FTP 服务器。

中间网络设备在此对话中起到哪三个作用（请选择三项。

）重新生成数据信号充当客户端或服务器提供传输消息的通道应用安全设置来控制数据流出现错误时通知其他设备用作消息的源或目标中间设备负责管理数据传输，包括跟踪数据路径，出现故障时寻找备用路径并通知其他设备，以及应用安全和优先级策略。

大学英语综合教程第四册uint1课后题参考答案

大学英语综合教程第四册uint1课后题参考答案P8 3. Questions on the text1. What was Dr. Rob Boll’s profession?He was a physician at a family practice.2. Why did so many non-congregation people attend the church’s annual fund-raising dinner?Because they could have a turkey feast at the dinner and help the church in some way.3. What is the Heimlich maneuver?It is an emergency treatment for suffocation when a person’s airway becomes blocked by a piece of food or other object.4. Who was the main assistant for Dr. Rob Boll in the operation?It was Colleen Rohrer.5. What instruments were used in the operation?A paring knife, a switchblade, a tracheotomy tube, and a resuscitator bag.6. Why did Dr. Rob Boll think the operation was a case of divine intervention?Because the tools he needed appeared and he succeeded in saving the lady as sort of a surgeon as if by magic.7. Why were Colleen and her family so grateful to Dr. Rob Boll? Because Dr. Boll saved Col leen’s mother-in-law and in the age of lawsuits, he was willing to put himself on the line.P10 5. Discussion1. Why was Dr. Rob Boll able to succeed in the emergency operation on the choking old lady?He made it through his knowledge and experience, thoughfar from sufficient, the others’ help, and a pinch of luck.2. What merit can we learn from Dr. Rob Boll?Though Rob Boll hadn’t done that kind of operation before, he was willing to accept the challenge in such an urgent situation. He risked being sued for his improper actions if the surgery failed. He showed a spirit of self-sacrifice and high professional ethics which we can learn.P10-11 6. Practice: interpreting罗布：看，她脸色发青，呼吸困难。

CCNA第四学期章节测试题答案c4

F列关于时分复用(TDM)的说法中哪两项正确？(选择两项。

)TDM依靠第3层协议工作。

可多个信道可通过单个链接传输。

口I原始数据流必须在目的地重建。

TDM方法取决于所用的第2层协议。

它可为多个信道的信息分配多条线路上的带宽。

分界点在数据通信物理电路中体现为什么？连接到In ternet的设备上的DTE/DCE接口防火墙或路由器所在的位置公共网络和私有客户网络分界的物理位置分配给存在交叉连接的物理网段的标记哪种串行通信DTE/DCE接口标准用于在LAN之间提供高达52 Mbps的高速连接且常用于许多高端Cisco路由器上？EIA/TIA 232 (RS-232)EIA/TIA 422 (RS-422)EIA/TIA 423 (RS-423)+ EIA/TIA-612/613 (HSSI)ITU V.35为什么串行连接比并行连接更适用于长距离传输？并行连接不支持差错校验。

并行连接可能发生过度衰减。

* 并行连接可能发生电线之间的串扰以及时滞。

并行连接仅可通过两条电线传输，因此传输数据的速度要慢很多。

下列关于HDLC封装的说法中哪三项正确？(选择三项。

)HDLC不支持CDP。

HDLC 和PPP相互兼容。

HDLC 支持PAP和CHAP身份验证。

Cisco路由器上实现的HDLC 是Cisco的专有技术。

"HDLC是Cisco路由器上的默认串行接口封装方法。

‘ HDLC使用帧定界符来标记每个帧的开头和结尾下列关于LCP的说法，哪三项是正确的？（选择三项。

）“ 它负责协商建立链路。

-I它会协商在PPP上运行的第3层协议的选项。

它在协商链路建立参数时使用MD5加密。

丁I它会在用户要求时或闲置计时器到期时切断链路。

丁|它能测试链路，确定链路质量是否足以开启该链路。

它会监控链路拥塞情况，并动态调整可接受的窗口大小。

LCP可协商哪两个选项？（选择两项。

）‘链路质量“身份验证动态流量控制压缩以及IP的网络层地址使用面向连接的通信方法还是无连接通信方法下列哪个PPP配置选项可用于在路由器的接口上建立负载均衡?回叫"多链路压缩. 错误检测网络控制协议可为PPP连接提供什么功能？' 进行错误检测建立和终止数据链路为PPP提供身份验证功能管理网络拥塞以及测试链路质量+允许多种第 3 层协议在同一物理链路上工作Router^ shaw internee seiialfl/OSciialO^) is up, lute protocol is upHardware is HD64570Entemet adiress is 10.140.1^24MTU 1SOO bytes,BW 1544 Khit,DLY 20000 usee^rtly255/255, had i/255Encapsulation PPP, loopback not set, keepalive set (IQ sec)LCP OpenOpen： IPCP.CDPCP38097packjets o ulput,2135597 bytes, 0 underruns0 output errors T0 collisioiis, 6045 interact resets0 output builer failure齢0 4utpvt buf^s^vapped out482 canier truisitionsDCD=up DSR=np DTR^np RTS=itp CTAup请参见图示。

计算机网络第四版(谢希仁)习题详细答案

计算机网络习题解答教材计算机网络谢希仁编著第一章概述习题1-01 计算机网络的发展可划分为几个阶段?每个阶段各有何特点?答: 计算机网络的发展过程大致经历了四个阶段。

第一阶段：(20世纪60年代)以单个计算机为中心的面向终端的计算机网络系统。

这种网络系统是以批处理信息为主要目的。

它的缺点是：如果计算机的负荷较重，会导致系统响应时间过长；单机系统的可靠性一般较低，一旦计算机发生故障，将导致整个网络系统的瘫痪。

第二阶段：(20世纪70年代)以分组交换网为中心的多主机互连的计算机网络系统。

为了克服第一代计算机网络的缺点，提高网络的可靠性和可用性，人们开始研究如何将多台计算机相互连接的方法。

人们首先借鉴了电信部门的电路交换的思想。

所谓“交换”，从通信资源的分配角度来看，就是由交换设备动态地分配传输线路资源或信道带宽所采用的一种技术。

电话交换机采用的交换技术是电路交换(或线路交换)，它的主要特点是：①在通话的全部时间内用户独占分配的传输线路或信道带宽，即采用的是静态分配策略；②通信双方建立的通路中任何一点出现了故障，就会中断通话，必须重新拨号建立连接，方可继续，这对十分紧急而重要的通信是不利的。

显然，这种交换技术适应模拟信号的数据传输。

然而在计算机网络中还可以传输数字信号。

数字信号通信与模拟信号通信的本质区别在于数字信号的离散性和可存储性。

这些特性使得它在数据传输过程中不仅可以间断分时发送，而且可以进行再加工、再处理。

③计算机数据的产生往往是“突发式”的，比如当用户用键盘输入数据和编辑文件时，或计算机正在进行处理而未得出结果时，通信线路资源实际上是空闲的，从而造成通信线路资源的极大浪费。

据统计，在计算机间的数据通信中，用来传送数据的时间往往不到10%甚至1%。

另外，由于各异的计算机和终端的传输数据的速率各不相同，采用电路交换就很难相互通信。

为此，必须寻找出一种新的适应计算机通信的交换技术。

1964年，巴兰(Baran)在美国兰德(Rand)公司“论分布式通信”的研究报告中提出了存储转发(store and forward)的概念。