八年级英语Chapter Three A dangerous servant沈阳牛津版知识精讲

初二英语Chapter Three: A dangerous servant沈阳牛津版【本讲教育信息】
一. 教学内容：
Chapter Three: A dangerous servant
二. 具体过程
情态动词用法
情态动词有can （could）, may （might）, must, have to, shall （should）, will （would）, dare （dared）, need （needed）, ought to等。

情态动词无人称和数的变化；不能单独使用，必须与其后的动词原形构成谓语
（一）can, could
1）表示能力（体力、知识、技能）。

Can you lift this heavy box（体力）
Mary can speak three languages.（知识）
Can you skate（技能）
此时可用be able to代替。

can只有一般现在时和一般过去式；而be able to则有更多的时态。

I’ll not be able to come this afternoon.
当表示“经过努力才得以做成功某事”时应用be able to，不能用can。

如：
He was able to go to the party yesterday evening in spite of the heavy rain.
2）表示请求和允许。

—Can I go now
—Yes, you can. / No, you can’t.
此时可与may互换。

在疑问句中还可用could, might代替，不是过去式，只是语气更委婉，不能用于一定句和答语中。

—Could I come to see you tomorrow
—Yes, you can. （No, I’m afraid not. ）
3）表示客观可能性（客观原因形成的能力）。

They’ve changed the timetable, so we can go by bus instead.
This hall can hold 500 people at least.
4）表示推测（惊讶、怀疑、不相信的态度），用于疑问句、否定句和感叹句中。

Can this be true
This can’t be done by him.
How can this be true
（二）may, might
1）表示请求和允许。

might比may语气更委婉，而不是过去式。

否定回答时可用can’t 或mustn’t，表示“不可以，禁止”。

—Might/ May I smoke in this room
—No, you mustn’t.
—May/Might I take this book out of the room
—Yes, you can. （No, you can’t / mustn’t. ）
用May I...？征询对方许可时比较正式和客气，而用Can I...？在口语中更常见。

2）用于祈使句，表示祝愿。

May you succeed!
3）表示推测、可能性（不用于疑问句）。

might不是过去式，它所表示的可能性比may小。

①He may /might be very busy now.
②Your mother may /might not know the truth.
（三）must, have to
1）表示必须、必要。

You must come in time.
在回答引出的问句时，如果是否定的，不能用mustn’t（禁止，不准），而用needn’t, don’t have to（不必）.
—Must we hand in our exercise books today
—Yes, you must.
—No, you don’t have to / you needn’t.
2）must是说话人的主观看法，而have to则强调客观需要。

must只有一般现在时，have to 有更多的时态形式。

①T he play isn’t interesting, I really must go now.
②I had to work when I was your age.
3）表示推测、可能性（只用于一定的陈述句）
①You’re Tom’s good friend, so you must know what he likes best.
②Your mother must be waiting for you now.
（四）dare, need
1）dare作情态动词用时, 常用于疑问句、否定句和条件从句中, 过去式形式为dared。

①How dare you say I’m unfa ir
②He daren’t speak English before such a crowd, dare he
③If we dared not go there that day，we couldn’t get the beautiful flowers.
2）need 作情态动词用时, 常用于疑问句、否定句。

在一定句中一般用must, have to, ought to, should代替。

①You needn’t come so early.
②—Need I finish the work today
—Yes, you must. / No, you needn’t.
3）dare和need作实义动词用时，有人称、时态和数的变化。

在一定句中，dare后面常接带to的不定式。

在疑问句和否定句中，dare后面可接带to或不带to的不定式。

而need 后面只能接带to的不定式。

①I dare to swim across this river.
②He doesn’t dare （to）answer.
③He needs to finish his homework today.
（五）shall, should
1）shall 用于第一人称，征求对方的意见。

What shall we do this evening
2）shall 用于第二、三人称，表示说话人给对方的命令、警告、允诺或威胁。

①You shall fail if you don’t work hard.（警告）
②He shall have the book when I finish it.（允诺）
③He shall be punished.（威胁）
（六）will, would
1）表示请求、建议等，would更委婉。

Will / Would you pass me the ball, please
2）表示意志、愿望和决心。

①I will never do that again.
②They asked him if he would go abroad.
3）would表示过去反复发生的动作或某种倾向。

would表示过去习惯时比used to正式，且没有“现已无此习惯”的含义。

①During the vacation, he would visit me every other day.
②The wound would not heal.
4）表示估计和猜想。

It would be about ten o’clock when she left home.
（七）should, ought to
1）should, ought to表示“应该”，ought to表示义务或责任，比should语气重。

①I should help her because she is in trouble.
②You ought to take care of the baby.
2）表示劝告、建议和命令。

should, ought to可通用，但在疑问句中常用should。

①You should / ought to go to class right away.
②Should I open the window
3）表示推测
should , ought to （客观推测）, must（主观推测）。

①He must be home by now. （断定他已到家）
②He ought to/should be home by now.（不太一定）
③This is where the oil must be.（直爽）
④This is where the oil ought to/should be.（含蓄）
（八）情态动词+不定式完成式（have done）
1）can / could + have done在一定句中表示“本来可以做某事”，是虚拟语气；在疑问句或否定句中表示对过去行为的怀疑或不一定, 表示推测。

①You could have done better, but you didn’t try your best. （虚拟语气）
②He can’t have been to that to wn.（推测）
③Can he have got the book（推测）
2）may / might +不定式完成式（have done）
表示对过去行为的推测。

不能用于疑问句中，没有虚拟语气的用法。

might所表示的可能性比may小。

①He may not have finished the work .
②If we had taken the other road, we might have arrived earlier.
3）must +不定式完成式（have done）
用于一定句中，表示对过去行为的推测。

意为“一定、想必”。

其疑问、否定形式用can，can’t代替。

参看1）can / could + have done表示推测。

①You must have seen the film Titanic.
②He must have been to Shanghai.
4）should +不定式完成式（have done）
用于一定句中，表示对过去行为的推测。

He should have finished the work by now。

表示“本应该做而实际上没有做某事”，其否定式表示某种行为本不该发生却发生了。

可以与ought to +不定式完成式（have done）互换。

①You ought to / should have helped him. （but you didn’t.）
②She shouldn’t have taken away my measuring tape, for I wanted to use it.
5）needn’t +不定式完成式（have done）
表示“本来不必做而实际上做了某事”。

You needn’t have watered t he flowers, for it is going to rain.
6）will +不定式完成式（have done）
主要用于第二、三人称，表示对已完成的动作或事态的推测。

He will have arrived by now.
【模拟试题】（答题时间：40分钟）
一. 单选：
1）You____ all those clothes! We have a washing machine to do that sort of thing
A. needn’t have washed
B. sho uldn’t have washed
C. must not have washed
D. can not have washed
2）John’s score on the test is the highest in the class; he____ last night.
A. should study
B. should have studied
C. must have studied
D. must have to study
3）The room is in a terrible mess; it ____cleaned.
A. can’t have been
B. shouldn’t have been
C. mustn’t have been
D. wouldn’t have been
4）Nobody knows how people first came to these islands. They ____ from South America on rafts.
A. must have sailed
B. can sail
C. might have sailed
D. should have sailed
5）Mary was not in her bedroom yesterday afternoon. She ____ in her classroom.
A. should have been
B. must have been
C. must be
D. should be
6）Bob said he was going to join our club but he didn’t. He ____ his mind.
A. can’t have changed
B. wouldn’t have changed
C. must have changed
D. shouldn’t have changed
7）You____ to town to see the film yesterday. It will be on TV tonight.
A. needn’t go
B. had better not go
C. should not go
D. needn’t have gone
8）We____ the letter yesterday, but it didn’t arrive.
A. must receive
B. ought to receive
C. must have received
D. ought to have received
9）With all the work on hand, he____ to the cinema last night.
A. mustn’t go
B. shouldn’t have gon e
C. could not go
D. couldn’t have gone
10）Eve was late for class again. She ____earlier.
A. should get up
B. must get up
C. need to get up
D. should have got up
11）I am feeling sick. I____ so much chocolate.
A. needn’t have eaten
B. couldn’t have eaten
C. mustn’t have eaten
D. shouldn’t have eaten
12）I didn’t send out my application form last week, but I ____.
A. had
B. would do
C. should have
D. might have to
13）Walking alone in the deserted village, John was scared. He thought he____ Tom to go with him.
A. might have asked
B. should asked
C. must have asked
D. should have asked
14）When I got to the cinema, the film had already started; I____ there earlier.
A. ought to get
B. ought to have got
C. must have got
D. must get
15）The road was muddy. It____ last night.
A. must rained
B. must have rained
C. must be rained
D. could have rained
16）She can speak quite fluent English. She____.
A. must been in the U.S.A. for some time
B. must have been in the U.S.A. for some time
C. should have been in the U.S.A. for some time
D. May be in the U.S.A. for some time
17）You should bear in mind that he is not so strong as he____.
A. was used to be
B. used to be
C. was used to
D. use to
18）“We didn’t see him at the exhibition yesterday.” “He ___it.”
A. mustn’t visit
B. can’t have visited
C. should have gone to see
D. may see
19）Mary ____my letter, otherwise she would have replied before now.
A. should have received
B. has received
C. c ouldn’t have received
D. ought to have received
20）I ____ you a valuable present for your birthday, but I was short of money.
A. would have liked to give
B. liked to give
C. have liked to give
D. would like to give
21）“Where ____ my umbrella” “Somebody ____ it away by mistake.”
A. is, must have taken
B. is, must take
C. have been, must take
D. is, takes
22）What ____ would happen if the director knew you felt that way
A. will you suppose
B. you suppose
C. do you suppose
D. you would suppose
23）Two eyes ____see more than one.
A. can
B. may
C. will
D. should
24）____ you continue in your efforts and achieve new and greater successes.
A. Would
B. Will
C. May
D. Should
25）We ought to help each other in our work, ____
A. oughtn’t we
B. should we
C. shouldn’t we
D. ought to we 26）You ____ your tooth pulled out before it rots completely.
A. had better got
B. had to get better
C. had better to get
D. had better get 27）When we got to the cinema, the film hasn’t started yet, so we ____.
A. needn’t hurry
B. didn’t need hurry
C. needn’t to hurry
D. needn’t have hurried
28）It was really very dangerous; you ____ him seriously.
A. might have injured
B. could injure
C. should have injured
D. must injure
29）As he had heart attack, he was told that he ____ continue the work.
A. needn’t
B. may not
C. mustn’t
D. can’t
30）An Englishman who ____not speak Italian was once traveling in Italy.
A. must
B. could
C. may
D. might
31）I ____like to make a suggestion.
A. could
B. would
C. must
D. might
32）I know things are hard with you, but you ____try to get over the difficulties.
A. can
B. may
C. must
D. ought
33）I can’t find the recorder in the room. It ____ by somebody.
A. may have been taken away
B. may leave
C. may take away
D. must have taken away
34）He ____the 9:20 train because he didn’t leave home till 9:25.
A. can reach
B. could catch
C. may not catch
D. couldn’t have caught
【试题答案】
1）A 2）C 3）A 4）C 5）B 6）C 7）D 8）D 9）D 10）D 11）D 12）C 13）D 14）B 15）B 16）B 17）B 18）C 19）C 20）A 21）A 22）C 23）A 24）C 25）A 26）D 27）D 28）A 29）C 30）B 31）B 32）C 33）A 34）D。