高中状语从句讲解及练习

合集下载

状语及状语从句(语法加练习完整讲解)

结果状语从句
The problem is so difficult that it will take us time to work it out. 这道题如此难以至于我们要用很多时间才能解决。
She is such a kind girl that everyone likes her. 她非常善良，以至于每个人都喜欢她。
not that...but that...(不是因为...而是因为)
条件状语从句
If you want to succeed, you'd better work hard. 如果你想成功，最好努力工作。 I'll come unless it rains. 除非下雨，否则我一定来。 You can borrow the book as long as you promise to keep i Ming studied so hard that he caught up with the others very quickly．李明学习如此努力，结果很快赶上了其他人。
6．程度状语： I nearly forgot what he had promised．我几乎忘记了他答应的事。
(2)如果动词前有一个或几个助动词，状语位于第一个助动词之后。 He has already had his lunch．他已吃过午饭了。
(3)如果动词是be，状语就放在be动词之后。 He is always at home. 他总是在家。
3.状语位于句末，这是状语的通常位置。
We get up at six in the morning. 我们早晨六点起床。
三、状语的分类：
状语按用途可分为：地点、时间、原因、目的、结果、条件、让步、程度、方式、伴随情况等几类。

完整版)高中英语状语从句讲解及练习

完整版)高中英语状语从句讲解及练习状语从句是指在句中作状语的从句，可以分为时间、条件、让步、原因、目的、结果、比较、地点、方式状语从句。

时间状语从句的连词有when、as、while、until、not…until、before、after、since、the minute、the moment、each、every、next、the first time等。

时间状语从句一般使用一般现在时或一般过去时。

当使用when、as、while这三个连词引导时间状语从句时，它们都表示“当…的时候”，但侧重点有所不同。

例如，当使用when引导时间状语从句时，从句的主语与主句主语相同，如果谓语动词是be动词，则从句主语和be可以省略。

而as则不仅表示“当…的时候”，还可以表示“一面…一面”或“随着”。

而while则强调主句的动作和从句的动作同时发生，从句一般用进行时，从句动词必须是延续性动词。

当使用until、not…until时，它们表示“直到…才”。

在肯定句中，主句常用延续性动词；在否定句中，主句常用短暂性动词。

需要注意的是，当not until…位于句首时，主句需要倒装。

例如，“Not until you had explained how did I manage to do it.”It was dark when he finally returned。

XXX the machine type upon seeing it。

As soon as I arrived home。

it began to rain。

Hardly had I arrived home when it began to rain。

XXX: real XXX: if。

even if/though。

unless/if。

not。

as long as/so long as。

as far as/so far as。

provided/providing(that)。

高中英语状语从句讲解与练习

高中英语状语从句讲解与练习高中英语状语从句一、时间状语从句1、when的用法（1）when既可引导一个持续性动作，也可引导一个短暂性动作，可用于表示主句和从句动作同时发生或从句动作先于主句动作，有时还可表示从句动作后于主句，意为“当……时候”。

（2）when在beabouttodo……when……，bedoing……when……，haddone……when……，beonone’sway……when……，beonthepointofdoing…when……等结构中作“那时突然”讲。

（3）when“既然、鉴于；尽管，虽然（位于主句之后）；如果”2、while的用法（1）则表示“当……时候”，鼓励的动作必须就是延续性的。

（2）用做同列连词，则表示相对关系“然而”。

（3）引导让步状语从句，相当于although,意为“虽然”，位于主句前。

（4）引导条件状语从句，相当于as/solongas，意为“只要”。

3、as的用法（1）则表示“当……时候”，特别强调同时出现，不所指先后。

（2）说明两种正在发展或变化的情况，表示“随着”，表示时间的推移。

（3）表示“一边……一边……”（4）强调两个动作紧接着发生。

（5）表示“虽然，尽管”（6）其他含义“正像，正如”，“做为”，“由于，因为”。

4、before的用法（1）一般意为“在……之前”“……才”，“……就”“还没有……”“免得”“不知不觉”“宁可，宁愿”，“否则，要不然”。

（2）itwillbe/was时间段before通常现在时/通常过去时。

在肯定句中，意为“多长时间之后才”；在否定句中，意为“用没法多长时间就”。

5、until和till（1）与肯定句连用，必须是延续性动词。

（2）与否定句属格，必须不为延续性动词，则表示“直至……才，在……之前不……”。

特别注意：notuntil可以用作特别强调句和倒装句强调句：itis/wasnotuntil…that…倒装句：notuntil放句首时，主句要部分倒装。

状语从句讲解与练习

状语从句讲解与练习一、时间状语从句定义：用从句来表达一件事情或一个行为发生的时间(一) before & afterbefore：“在……之前”，主句动作发生在从句动作之前[主前从后]after：“在……之后”，主句动作发生在从句动作之后[主后从前]He called me after he finished his homework.He had learned English for three years before he went to London.(二)as soon as 一……就…… [主将从现]表示从句动作一发生，主句动作马上就发生。

I'll tell her everything as soon as she comes back.As soon as I reached Canada, I rang him up.(三) since 自从(1) 主句【现在完成时】+ since时间状语从句【一般过去时】He has gone abroad since he was 20.(2) It’s + 一段时间+ since时间状语从句【一般过去时】It is 10 years since we became friends.(四) until(1) 用于肯定句中，表示主句的动作一直持续到从句动作发生或状态出现时为止。

一般可译为“直到……为止”。

主句的动词必须是延续性的。

He will stay here until his mother comes back. [主将从现](2) until用于否定句中，表示主句的动作在从句的动作发生之后才开始。

一般可译为“直到……才……”或“直到……之前不要……” 。

主句的动词多为非延续性。

Don”t get off the bus until it has stopped.The little girl didn’t stop crying until she saw her mom.(五) when & while & as(1) 理论基础①三者都可表示“当……时”② while只接持续性动词，when/as持续、短暂都可以接③while 多用于进行时态，when多用于一般时态(2) 一般时while进行；进行when一般时The telephone rang while I was taking a bath.I was reading a newspaper when he came in.(3) 事件对比用while（然而；却）Father was preparing a report while I was playing PC games.He likes coffee while she likes tea.(4) “随着”/“一边…一边”用asThings are getting better and better as time goes on.She sang as she went along.二、原因状语从句because 因为（不与so连用）(1) because &because ofbecause引导原因状语从句because of 是介词短语，后跟n./pron./V-ing，句中作原因状语-- Why didn't he come here?-- He didn’t come here because he was ill.-- He didn’t come here because of his illness.(2) because & for & since & asbecause 语气最强烈；for放句中，用来表示一种附带或补充解释、说明；since & as 通常放句首，作“既然”讲。

高中英语状语从句专项讲解及练习（有答案）

高中英语状语从句专项讲解及练习（有答案）状语从句1、地点状语从句地点状语从句表示地点、方位，这类从句通常由where, wherever, anywhere, everywhere引导。

Where there is a will, there is a way.有志者，事竟成。

They will go where they are happy.他们想到他们觉得快乐的地方去。

We must camp where we can get water. 我们必须在能找到水的地方露营。

地点状语从句与定语从句的区别:在于分句在句中作什么成分。

作状语，则是状语从句；作定语修饰名词，则是定语从句。

where引导定语从句时，从句前应有一个表示地点的名词作先行词；而状语从句前则无需先行词。

如：Go back where you came from.(where引导地点状语从句）Go back to the village where you came from.(where引导定语从句，修饰village)We went home, where we had dinner. (where引导定语从句，修饰home)2、原因状语从句原因状语从句一般由because(因为)，since(既然)，now that(既然，因为)，as(由于)等连词引导。

（1）because表示直接的原因，表示原因的语气最强，常表示必然的因果关系。

回答why引起的特殊疑问句，只能用because。

Jane wore a raincoat because it was raining.因为天下雨，所以詹穿着雨衣。

He is absent today because he is ill.他今天缺课，因为他病了。

（2）since表示对方已经知晓、无须加以说明的原因或事实，语气比because稍弱。

I'll do it for you since you are busy.既然你忙，我来替你做吧。

状语从句课件讲解和练习

As soon as he es, I’ll tell him. The moment I saw him, I recognized him. I left immediately the clock struck 5.
2 on / upon doing / on upon one’s +n
On arriving at the station, the thief was arrested. On his arrival in Paris, he was recognized as a famous person.
1 as 引导的让步从句要倒装,句型为：形容词/ 副词/ 名词不带冠词 / 动词原形 +主语+谓语 Young as he is, he knows a lot. Much as I like it, I can’t afford it. Farmer as he is, he is well-educated. Try as I might, I couldn’t lift the stone. 2 although不倒装, though可倒装也可不倒装, as 必须倒装
We didn’t go home _____ we finished the work. A. since B. until C. because D. though
It was not ______ she took off her dark glasses ______ I realized she was a famous film star. A. when; that B. until; that C. until; when D. when; then
另外, when/while还作并列连词,连接并列分句, while表示 “而,可是”如: I like reading while my wife enjoys watching TV. when表示 “就在这时” 在下列结构中,表示某件事正在发生或刚刚发生,另一动作同时发生。

高中状语从句综合讲解及练习

高中英语状语从句★注意：1.需要倒装的情况：1) hardly, scarcely 或no sooner等置于句首例如：我一到家就开始下雨了。

Hardly / Scarcely had I got home when it began to rain. No sooner had I got home than it began to rain.2) Not until …在句首，主句用倒装。

例如：直到19 世纪初，人类才知道热能是什么。

直到我开始工作，我才认识到了我已蹉跎了几多岁月。

Not until the early years of the 19th century did man know what heat is.Not until I began to work did I realize how much time I had wasted.2.When,as,while用法区分：1)当从句的动作发生于主句动作之前，只能用when 引导这个从句，不可用as 或while。

例如：When you have finished your work, you may have a rest.2)如从句表示"随时间推移"，连词能用as，不用when 或while。

例如：As the day went on, the weather got worse.★练习1. last week, she lived a quiet and happy life in that area.A. Not until the earth-moving machines cameB. The earth-moving machines cameC . Until the earth-moving machines came D. Then came the earth-moving machines2. —when has the country been open to international trade?—1978, I suppose.A .Since B.In C.From D.After3. The project won’t carry on we can get financial aid from the government.A .unless B.though C.whether D.until4. The number of women dying from breast cancer has fallen to its lowest level ____ records began in 1971.A. whenB. before C . since D. after5. Nancy enjoyed herself so much she visited her friends in Sydney last year.A. thatB. which C . when D. where6. You see the lightning it happens, but you hear the thunder later.A . the instant B. for an instant C. on the instant D. in the instant7. they visited the Science Museum, they showed great interest in everything they saw.A . The first time B. For the first time C. At first D. At the first time8.How long do you think it will be we can find a new water source?A. after B . before C. when D. since9.We were beginning to discuss suddenly a great earthquake happened.A . when B. while C. until D. before10.No sooner had rescue forces reached the earthquake-stricken area they got down to saving those buriedbeneath the debris.A. whenB. then C . than D. until11.I found her nice and honest I saw her.A. for the first time B . the first time C. on the first time D. at first★注意：For和because用法区分For引导的从句并不说明主句行为发生的直接原因，只是提供一些补充说明，且不可位于主句前。

状语及状语从句(语法加练习完整讲解).ppt

4．动词不定式（或不定式短语）： He went to see a film ．他看电影去了。 My father was surprised to hear the news ．我父亲听到这个消息，感到惊奇。
5．分词（短语）： He sat there reading a novel ．他坐在那儿看小说。 The students went away laughing．学生们笑着走开了。
2023最新整理收集 do something
The Adverbial 状语
ห้องสมุดไป่ตู้ 一、什么是状语
修饰动词、形容词、副词或整个句子，说明动作或状态特征的句子成分，叫做状语。
1. 状语修饰动词 Silently she went away. 她悄悄地走开了。
2. 状语修饰句子 Sadly, he will not be there. 令人伤心的是，他将不会在那里了。
The Adverbial Clauses 状语从句
从状种九
时间状语从句地点状语从句原因状语从句条件状语从句让步状语从句结果状语从句目的状语从句方式状语从句比较状语从句
时间状语从句
I will discuss this with you when we meet. 我们见面时再与你讨论这件事。
(2)如果动词前有一个或几个助动词，状语位于第一个助动词之后。 He has already had his lunch ．他已吃过午饭了。
(3)如果动词是 be，状语就放在 be动词之后。 He is always at home. 他总是在家。
3.状语位于句末，这是状语的通常位置。 We get up at six in the morning . 我们早晨六点起床。

高中英语状语从句讲解及练习精编版

高中英语状语从句讲解及练习公司内部编号：（GOOD-TMMT-MMUT-UUPTY-UUYY-DTTI-状语从句状语从句在句中作状语，可分为：时间、条件、让步、原因、目的、结果、比较、地点、方式状语从句。

一、时间状语从句引导时间状语从句的连词有：when, as, while, until, not…until, before, after, since, the minute, the moment, each( every, next, the first) time等。

时间状语从句中一般用一般现在时或一般过去时。

1．When , while, as都可解释为“当```的时候”但侧重点有所不同。

1)WhenEg: When I arrived home , I had a little rest.注意点：when 从句的主语与主句主语相同，谓语动词是be 动词时，从句主语和be可以省略。

Eg: When (she was) walking along the street, she met her class teacher.2)AsAs 除了表示“当```的时候”，还可表示为“一面```一面”，“随着”Eg: He sang as he danced.(一面```一面)You will grow wiser as you grow older.(随着)3)While表示“当```的时候”强调主句的动作和从句的动作同时发生，从句一般用进行时，从句动词必须是延续性动词。

Eg: While we were working, they were having a rest.While (they were) having a discussion, they got very confused.注意点：while 有对比的含义，解释为“然而”。

eg: I prefer black tee, while he likes coffee.2．until, not…until表示“直到```才”,在肯定句中主句常用延续性动词；在否定句中主句常用短暂性动词。

高考状语从句讲解和练习题

⾼考状语从句讲解和练习题定义——在复合句中由从句表⽰的状语称作状语从句，状语从句由从属连词引导，也可以由⼀个起连词作⽤的词组引导，有时甚⾄不需要连词⽽直接和主句连接起来。

类型——时间、地点、原因、结果、条件、⽬的、让步、⽅式、⽐较状语从句。

1.引导词when, while, as, as soon as, once, before, after, every time, each time, since, whenever, ever since, until ,till等。

2.whenever, each time, every time的⽤法。

注：whenever=no matter whenevery time / each time 每次，whenever 每当······时，表⽰习惯性、经常性的动作。

Whenever we met with difficulties, they came to help us.Each time he came to town he would visit our school.Eevery time I went to his house, he was out.注：whenever=no matter whenwhenever既可以引导时间从句也可引导名词性从句，no matter when只可以引导时间状语从句。

It does not matter whenever the party begins.3.before的汉英表达1）before的基本含义是“在·····以前”The train had left before he got to the station.注意：与before对应的是after引导的时间状语从句，表“在·····之后”。

状语从句讲解及习题附答案

状语从句讲解及习题附答案（一）状语从句概述定义状语从句用作状语，是起副词作用的句子。

位置状语从句可以放在主句之前，也可以放在主句之后，时间、条件、原因和让步状语从句放在句首时需要用逗号和主句隔开。

分类根据其作用可以分为时间、地点、原因、条件、目的、让步、方式和比较等状语从句。

作用它可以修饰谓语、非谓语动词、定语、状语和整个句子。

（二）状语从句详解1. 时间状语从句引导词用法示例when 意为“当…的时候”。

When引导从句的谓语动词可以是延续性动词，也可以是瞬间动词。

并且when有时表示“就在那时”A liar is not believed when he speaks the truth.说谎者讲真话时也没有人相信。

When he arrives, I’ll call you. When you laugh and smile, your body relaxes.while 意为“在…的时候，在…的同时”。

While引导从句的谓语动词必须是延续性的，发生时间较长，并强调主句和从句的动作同时发生（或者相对应）。

While有时还可以表示对比。

While I was standing at the window, I saw several boys running along the street.While John was watching TV, his wife was cooking.as 意为“一边…一边…”。

As引导的动作是延续性的，发生时间较短，一般用于主句和从句动作同时发生；as也可以强调一前一后。

The writer was angry as he was travelling on a train to London because someone had invaded his “space”.He smiled as he stood up.after 意为“在…之后”。

高中时间状语从句及练习(含解答)

高中时间状语从句及练习(含解答)状语从句是用来修饰主句中的动词、形容词或副词等的从句。

当状语从句放在主句之前时，通常需要用逗号分隔；而当放在主句之后时，则不需要逗号。

根据其意义和作用，状语从句可分为时间、原因、地点、条件、让步、目的、结果、方式和比较等九种类型。

1.时间状语从句时间状语从句用于表示主句动作发生的时间，通常由when、while、as、before、after、till (until)、once、by the time、as soon as、no sooner。

than和hardly。

when等引导词，以及名词词组XXX等构成。

其中，when表示“在……的时候”，强调“特定时间”。

例如：When spring came。

he felt like taking a trip.When he was eating his breakfast。

XXX.需要注意的是，连词when在状语从句中还有其他含义。

比如，它可以表示突然发生的事，含义为“（正在……时）忽然”；可以表示过早发生某事，意为“（还没……）就”；还可以表示“在……的情况下”，通常译为“虽然”、“既然”、“如果”等。

举个例子：I was just coming along to see you when I ran into Wilson.I hadn’t been reading for half an hour when I heard steps outside.She refuses help when (although) she has many friends.Why do you walk when (since) you have a car?How can I make them understand if they refuse to listen to me。

It's frustrating when you XXX。

高中英语状语从句知识点及练习

高中英语---状语从句一、概念：状语通常由副词、介词短语、动词不定式、分词和从句等担当。

?? ???状语从句主要用来修饰主句或主句的谓语。

一般可分为九大类，状语从句的关键是要掌握引导不同状语从句的常用连接词和特殊的连接词。

二、分类及使用1.?时间状语从句?(1)?when ?①.when引导的时间状语从句，其动词既可以是延续性动作的动词，也可以是瞬间性动作的动词，可以表示主句的动作和从句的动作同时发生，或从句的动作发生在主句的动作之前。

?when?you?apply?for?a?job,?you?must?present?your?credentials.?②?when还可表示just?then（正在那时）的意思，此时所引导的从句放在主句之后。

?we?were?about?to?start?when?it?began?to?rain.?(2)?as引导的时间状语从句?as侧重表示主句和从句的动作并相发生,翻译成一边，一边。

? We?were?having?breakfast?as?she?was?combing?her?hair.(3)?while “在…期间”，所引导的从句的动作是延续性的，并表示和主句的动作同时发生。

? ?(4)?before引导?①?before“在…之前”?I’ll?be?back?before?you?have?left.??②?before“…之后才”?It?may?be?many?years?before?we?meet?again.??(5)?as?soon?as/once/directly/the?instant等引导as?soon?as?是最常见的表示“一…就”的从属连词，其他连词还有immediately，instantly，the?instant?(that)，the?minute(that)?，the?moment(that)等，它们通常都可与as?soon?as换用。

高考英语状语从句和动词时态详解及练习

、考点聚焦1、时间状语从句(1) as、when、while 用法一览表。

（2）引导时间状语从句的连接词除上述外还有：①till, not p n til …,un til, before, sinceDon' t get off the bus un til it has stopped.He waited for his father until（till）it was twelve o ' clock.before的有关句型It will be +段时间+before+从句（一般现在时）要过…..才”It will be five years before he retur ns from En gla nd.It won 'be long before +从句（一般现在时）不久…就会”It won 'be long before he recovers from the injury.It was 3 years before he rega ined the love from his pare nts.It was n 'tl ong before the whole n ati on rose up to drive the en emy out of their coun try.He rang off before I could an swer it.②hardly / scarcely … when, no sooner …than, as sooona& 表示一......... 就”As soon as I have finished it , I ' ll give yu a call.Once you show any fear, he will attack you.We had hardly got / Hardly had we got into the country whe n it bega n to rain.No sooner had he arrived / He had no sooner arrived than she started complaining.③directly, immediately, the mome nt, the minute that 一...... 就He made for the door directly he heard the kno ck.④each time, every time, next time, any time ,by the timeEach time he came to my city, he would call on me.⑤the day, the time, the first（sec ond, third …）time, the spri ng （summer, autinter）His mother died the spri ng he retur ned.注意：表示未来情况，主句用将来时，从句用现在时。

高中英语状语从句练习与讲解含答案

高中英语状语从句练习与讲解状语从句状语从句在句中相当于副词做状语,又叫副词性从句。

状语从句分为时间状语从句、条件状语从句、地点状语从句、原因状语从句、目的状语从句、让步状语从句、结果状语从句和比较状语从句。

掌握状语从句应当引导词入手，注意引导词的词义,引导状语从句的引导词都有词思,所以,了解引导词的意思尤为重要。

引导词按意义分为九类:1)时间when , as , while , till , until , before, after , since2)地点where3)原因because , as , since , now that4)条件if , unless , once .so (as)long as . in case5)让步though , whatever (--ever) as, even though, even if6)目的so that, in order that7)结果so ... that8)比较than, as .. as9)方式as , as if例如:1．I fell asleep when ( as , while ) he was doing his exercises .他正作练习时我睡着了。

（时间状语从句）2．When he arrived in Shanghai , his mother met him at the station .他到上海时，他妈妈到车站接他。

（时间状语从句）3．She always sings as she walks .她总是一边走一边唱。

（时间状语从句）4．I waited until he had finished his work .我等到他做完活。

（时间状语从句）5．It was not long before he told me about this affair .不久，他就告诉我这件事。

（时间状语从句）6．He has worked very hard since he entered the factory .自从他进厂，工作一直很努力。

时间状语从句+习题练习(含答案)

专题: 时间状语从句在下列空格中填入适当连词。

1._________he comes tomorrow,I will ask where he has been.2._________he was speaking,everybody listened carefully.3.I saw her just now_________she was getting off the train.4.Have a good look at that man________you pass him.5.It was already eight o'clock_________we got there.6.I was about to go out_________a visitor came.7.We'll go to the country at the beginning of June,_________the summer harvest will start.8.He learned to speak German_________he was in Berlin.9.Henry is in charge of the office________Mr.Smith is away.10.I listen to the recorder_________I have time.11.He had learned Chinese_________he came to China.12._________the work was done,we sat down to sum up experience.13.I haven't seen him_________he moved to the other side of the town.14.I waited________ he came back.15.I didn’t recognize him________he took off his eyeglasses.16.She likes everything to be in place________she starts to work.17.The thieves ran away_________they caught sight of the police.18.They decided to go back home_________their money ran out.19.__________I get to the airport,I will phone you to pick me up.20.They were about to leave______it began to rain.Keys:1.When2.While/When3.as4.when/as5.when6.when7.when8.while9.whi le10.whenever11.before12.After13.since14.till/until15.until16.before17.as soon as18.before19.As soon as20.when。

高中英语状语从句讲解及练习(含答案)

状语从句状语从句在句中作状语，可分为：时间、条件、让步、原因、目的、结果、比较、地点、方式状语从句。

一、时间状语从句引导时间状语从句的连词有：when, as, while, until, not…until, before, after, since, the minute, the moment, each( every, next, the first) time等。

时间状语从句中一般用一般现在时或一般过去时。

1．When , while, as都可解释为“当```的时候”但侧重点有所不同。

1)WhenEg: When I arrived home , I had a little rest.注意点：when 从句的主语与主句主语相同，谓语动词是be 动词时，从句主语和be可以省略。

Eg: While we were working, they were having a rest.While (they were) having a discussion, they got very confused.注意点：while 有对比的含义，解释为“然而”。

eg: I prefer black tee, while he likes coffee.2．until, not…until表示“直到```才”,在肯定句中主句常用延续性动词；在否定句中主句常用短暂性动词。

高考英语状语从句详解习题加答案

高考英语状语从句详解习题加答案状语从句1. 在主从复合句中修饰主句中的动词，形容词，副词等的从句叫状语从句。

可分为，时间状语从句，地点状语从句，原因，目的，结果，条件，让步，比较和方式状语从句。

2. 时间状语从句起时间状语作用的句子；可放在句首，句中和句尾常用引导词：when，while, as, after, before, since, till, until, the moment, hardly … when , no sooner … thanwhen, while, as的用法1) when 用法最广，常可代替while和as, 在while 引导的从句中，动词只能是延续性的When the fire broke out, all the students were sleeping soundly.The telephone rang while I was taking a bath.2) 当两个表示时间延续的动作同时发生而又有对比意味的时候，用while，在这样的复合句中，主句从句的时态通常是相同的。

Father was preparing a report while I was playing PC games.3) 常用as的情况：一边…一边；表示随着短暂动作的发生，另一行为伴随发生As he talked on, he got more and more excited.They talked as they walked along the river.My cap was blown away as I sat down.until和till的用法表示“一直到…”时，主句和从句都用肯定式；I will wait until/ till the concert is over.表示“直到…才…”是，主句用否定，从句用肯定式。

They can’t go until Sunday.since的用法He has written to me frequently since he was ill. 自从他病好以来，他常写信给我。