(一)when, while 和 as 引導時間狀語從句的用法
一、when 的用法
如果只從現象來看，when 從句用的最多的是一般過去時，而主句的時態沒有限制,根據具體情況而定。
1. When he was a child he was always trying out new ideas.他小時候就常常試驗一些新的設想。
2. When she came into my room, I was just reading a book. 她走進我房間時，我正在看書。
3. Were you writing when the teacher came in? 老師進來的時候，你在寫信嗎?
4. Sorry, I was out when you called me. 對不起，你打電話來的時候我出去了。
5. He was on the point of leaving when someone knocked at the door.他正要走，這時有人敲門。
6. I thought of it just when you opened your mouth. 就在你要說話的時候，我也想到了。
7. I had hardly[scarcely] closed my eyes when someone knocked at the door.我剛一閉上眼，就有人在敲門了。
根據以上的例句，我們可以總結出一點：when 從句的A事件，相當於另一個事件B發生的時間點。也就是說，when 從句的重點不在動作本身發生的狀態，而只是把它作為一個時間點，所以when 多數情況下用的是一般過去時，則不用正在進行時。因為如果用正在進行時，它表示的就是一段時間而不是一個時間點了。根據這一點，有的文章補充說：when 從句的動詞大多是瞬時動詞。這種說法也可以參照。
實際上，when 從句也可以有其它的時態，但幾乎也不用進行時，因為它也只是作為一個時間參照點。例如：
1. When I got to the airport, the guests had left. 當我趕到飛機場時，客人們已經離開了。
2. When he had finished his homework, he took a short rest.當他完成作業後，他休息了一會兒。
3. Why do you want a new job when you have got such a good one already?你已經找到如此好的工作，為何還想再找新的?
4. You shall borrow the book when I have finished reading it.在我讀完這本書後，你可以借閱。
5. When the manager comes here for a visit next week, I’ll talk with him about this.下周，經理來這參觀時，我會和他談談此事。
二、while 的用法
相比於when 來說，while 從句的側重點就不一樣了。while 從句的側重點在於描述動作正在發生的狀態，它的意思是：當while 事件正在發生的時候，另一件事如何如何。所以，while 從句一般用的是正在進行時。而另一件事的狀態沒有硬性的要求，根據具體情況而定。例如：
1. While my wife was reading the newspaper, I was watching TV.當妻子正在看報紙的時候，我正在看電視。
2. While Jim was mending his bike, Lin Tao came to see him.正當吉姆修自行車時，林濤來看他。
3. While they were talking, the bell rang. 正在他們談話的時候，上課鈴響了。
4. You can’t do your homework while you’re watching TV.你不能一邊看電視一邊做家庭作業。
5. While John was sitting biting his nails, I was working out a plan to get us home.約翰坐在那裡咬指甲時，我正在制定一個回家的計劃。
從時間的角度來看，while 表示的是一段時間，是一個過程。這是while 的側重點。因此，如果含有“一段時間”的含義的時候，就可以用while。
6. Strike while the iron is hot. 趁熱打鐵。
這句話中，是說趁著鐵是熱的這段時間，趕緊打鐵。如果換成 when 意思就變了，相當於說鐵只熱了一下，打一下，然後鐵就冷了。這顯然不符合文意。
再例：
—I'm going to the post office.
—While you're there, can you get me some stamps?
三、as 的用法
as 從句表示的也是一件事情正在發生，另一件事也正在進行當中。但與 while 從句不同的是，as 從句用的一般不用正在進行時，而只是一般過去時。as 從句一般可以翻譯成“邊……邊……”。例如：
1. As my mother sang those old songs, tears ran down her cheeks.當我媽媽唱起那些老歌時，眼淚順著她的臉頰流了下來。
2. The students took notes as they listened. 學生們邊聽課邊做筆記。
3. As we talked >我們繼續往下談的時候，他越來越興奮。
4. The little girls sang as they went. 小姑娘們一邊走，一邊唱。
5. Just as he caught the ball, there was a tearing sound.當他抓住球的時候，有一種撕裂的聲音。
as 表達的事件，往往只是主句動作發生的背景或條件時，as 只是一個次要的時間說明，不像while 從句有強調 while 動作本身的意思。因此，as 常常翻譯成“隨著……”之意。
例如：
1. As the time went >，the weather got worse. 隨著時間的推移，氣候更加糟糕。
2. The atmosphere gets thinner and thinner as the height increases.隨著高度的增加，大氣越來越稀薄。
3. As years go by，China is getting stronger and richer.隨著時間一年一年過去，中國變得越來越富強了。
少數情況下，如果強調動作正在發生，as 從句也可以用正在進行時。這只能算是特例了。
1. The sad mother sat on the roadside, shouting as she was crying.傷心的媽媽坐在路邊，邊哭邊叫喊。
2. As we were going out, it began to snow. 正當我們出門時，雪開始下起來。
3. He came in as I was going to bed. 我正要上床睡覺，他進來了。
四、when, while, as 的互換
如果從句動作和主句動作同時發生，並且從句動作為延續性動詞時，when，while，as 可以互換使用。
1. When /While /As we were dancing, a stranger came in. 當我們跳舞時，一位陌生人走了進來。[dance 為延續性動詞]
2. When /While /As she was making a phone call, I was writing a letter.當她在打電話時，我正在寫信。[make為延續性動詞]
3. While/When/ As I was walking down the street, I noticed a police car in front of thebank.我順著馬路往前走時，發現銀行門前停著一輛警車。
五、比較while, when, as
1)as, when 引導短暫性動作的動詞。
例如：Just as / Just when / When I stopped my car, a man came up to me.我剎車後，有一個人向我走來。
2)當從句的動作發生於主句動作之前，只能用when 引導這個從句，不可用as 或 while。
例如：When you have finished your work, you may have a rest.幹完活後，你可以休息一下。
3)從句表示“隨時間推移”連詞能用as，不用when 或while。例如：As the day went > 日子一天天過去，天氣越變越壞。
(二)before和after引導的時間狀語從句
Before是主句動作發生在從句的前面。注意before引導的從句不再用否定式的謂語，並且當before引導的從句位於主句之後，有時譯成“就，才”。還要注意主句和從句之間的時間關係。當主句用將來時，從句總是用現在時;如果before引導的從句謂語用的是過去時，則主句動詞多用過去完成時，這樣以便體現動作發生的先後。
After表示主句動作發生在從句動作之後。主句和從句的動作的時間關係正好與before引導的從句相反。例如：
It will be four days before they come back. 他們要過四天才能回來。
Einstein almost knocked me down before he saw me.愛因斯坦幾乎把我撞倒才看到我。
My father had left for Canada just before the letter arrived.我父親恰好在信到之前去加拿大了。
They had not been married four months before they were divorced. 他們結婚還不到四個月就離婚了。
After you think it over, please let me know what you decide.你仔細考慮過以後，告訴我你是怎樣決定的。
After we had finished the work, we went home.完成工作之後，我們回家了。(從句用過去完成時，主句用一般過去時)
(三)比較until和till 的用法
此兩個連詞意義相同。肯定形式表示的意思是“做某事直至某時”，動詞必須是延續性的。否定形式表達的意思是“直至某時才做某事”。動詞為延續性或非延續性都可以。正確使用這兩個連詞的關鍵之一就在於判斷句中的動詞該用肯定式還是否定式。
肯定句：I slept until midnight. 我一直睡到半夜時醒了。
Wait till I call you. 等著我叫你。(在肯定句中可用before代替。
例如
：Let's get in the wheat before the sun sets.)
否定句：She didn't arrive until 6 o'clock. 她直到6點才到。
Don't get off the bus until it has stopped. 公共汽車停穩後再下車。
I didn't manage to do it until you had explained how. 直到你教我後，我才會做。
區別：1)until可用於句首，而till通常不用於句首。
例如：Until you told me, I had heard nothing of what happened. 直到你告訴我以前，出了什麼事我一點也不知道。
2)until when 疑問句中，until要放在句首。
例如：
---Until when are you staying?
你呆到什麼時候?
--- Until next Monday. 呆到下周一。
注意：否定句可用另外兩種句式表示。
3)Not until…在句首，主句用倒裝。
例如：
Not until the early years of the 19th century did man know what heat is. 直到19 世紀初，人類才知道熱為何物。
Not until I began to work did I realize how much time I had wasted. 直到工作，才認識到我已蹉跎了許多歲月。
4)It is not until… that….
例如：It was not until I began to work that I realized how much time I had wasted.
(四)巧辨before和until
在日常英語教學中，我們遇到學生問這樣的一些問題：
1.He will spend six hours at his desk____he finishes his composition.
A.before B.until C.after D.when
2.The bike hit the tree____I could get off.
A.when B.before C.while D.until
3.I knocked at the door for more than five minutes____Mrs white answered it.
A.until B.when C.after D.before
4.It was____yesterday____be____the secret.
A.not until;that;knew B.until;when;knew
C.not before;that;found D.before;that;didn't find
怎樣才能清楚地解釋其選擇的原因，這就涉及到until與before的區別問題。
實際上，只要我們把握住兩者使用時本身的含義及主句動詞是終止性的，還是延續性的，肯定式，還是否定式兩大點，就能容易地解決這類問題。現詳細闡明如下：
一、在下列情況下，兩者可互換用，但含義略有不同
before表示“在……之前”的意思，強調時間先後關係;而until表示“直到……才”的意思，主句是肯定句則表示主句動作的終止時間;主句是否定句則強調主句動作的起始時間。
1.主句為否定式終止性謂語動詞。常見的動詞是open,start,leave,arrive,finish, stop等。例如：
(1)The noise of the street didn't stop until/before it was midnight.
(2)The children won't come back until/before it is dark.
(3)I didn't leave the lovely boy until/before his mother came home.
2.主句為肯定式、延續性謂語詞，這類動詞用stand,stay,talk,be,wait等。例如：
(1)He lived with his parents until/before he graduated from school.
(2)I will wait until/before he comes to my help.
(3)I shall stay heer until/before you come back.
二、在下列情況下，用before不用until
1.主句這肯定式、終止性謂語動詞，只用before。例：
(1)He fell asleep before I could take off his clothes.
(2)We arrived there before it atarted to rain.
(3)The holiday came to the end befor I knew it.
(4)He almost knocked me down before he saw me.
2.主句謂語動詞強調動詞的遲緩性，只用before，常伴有時間段狀語或時間段暗示。例：
(1)It was quite some time before he found the elephant at all.
(2)We had walked a long way before we found some water.
(3)We had sailed for two days before we saw the land.
(4)The fire lasted about four hours before the firefighters could
countrol it.
(5)It was midnight before my brother came home.
(6)It was three months before they met again.
3.如果強調從句謂語動作未發生，就發生主句謂語動作，只用before。常譯為“未及”，“不”或“不等……就”。例：
(1)We can leave early in the morning before it gets too hot.
(2)I must write it down before I forget it.
(3)We do want to buy something now before prices go up.
4.表“與其說……倒不如”，“與其……毋寧……”只用before。例：
(1)I would give up my job before I'd agree to be dismissed.
(2)He will die of hunger before he will steal.
5.在某些特定句型中用before。例如：
(1)It was not long before the whole country rose up.
(2)It will probably not be long before they understand each other.
三、下列情況一般區別用until
1.主句是持續性謂語動詞時，肯定、否定都可以，但意義完全不同。肯定表動作終止，而否定表動作開始。例如：
(1)We discussed the problem until/before he came back.我們一直討論到他回 來。
(2)We didn't discuss the problem until he came back.我們一直等到他回來後才討論問題。
2.not…until句型儘管在某些情況下可與before互換用，但在強調句中一般仍用until。
例如：
(1)It was not until he told me that I knew it.
(2)It was not until he finished his homework that he went home.
綜上所述，前面的4條選擇題中，第1、3題強調動作發生的遲緩性應選before。第2題表動作未及發生就發生主句動作也應選before。第4題為強調句應選A項。
(五)其他時間狀語從句的用法
1.由since引導的時間狀語從句。
since引導的從句的謂語動詞可以是延續性的動詞，又可以是瞬時動詞。一般情況下，從句謂語動詞用一般過去時，而主句的謂語動詞用現在完成時。但在It is +時間+since從句的句型中，主句多用一般現在時。例如：
I have been in Beijing since you left. 自從你離開以來，我一直在北京了。
Where have you been since I last saw you? 自上次我和你見面以後，你到哪裡去了?
It is four years since my sister lived in Beijing. 我妹妹不在北京住有四年了。
It is five months since our boss was in Beijing.我們老闆離開北京有五個月了。
知識擴展
1. It is since從。。。以來多長時間了(因為since +從句或名詞，表示一段時間)
It is five years since we met last time.從我們上次見面已經五年了。
2. It is +before…(。。。才)It was a long time before I went to sleep again.過了很長時間我才睡著。It was an hour before(=until) the police arrived.過了一個小時，警察才來。
3.由as soon as, immediately, directly, instantly, the moment, the instant, the minute, 等引導的時間狀語從句。這些連詞都表示“一……就”。
例如：I will go there directly I have finished my breakfast. 吃完早飯，我立即到那裡去。
The moment I heard the news, I hastened to the spot.我一聽到消息，馬上趕到了出事地點。
As soon as I reach Canada, I will ring you up. 我一到加拿大，就給你來電話。
4.由by the time引導的時間狀語從句。注意時態的變化：在一般情況下，如果從句的謂語動詞用一般過去時，主句的謂語動詞用過去完成時;如果主句的謂語動詞用一般現在時，主句的謂語動詞用將來完成時。
例如：By the time you came back, I had finished this book.到你回來時，我已經寫完這本書了。
By the time you come here tomorrow, I will have finished this work. 你明天來這兒的時候，我將已經完成此工作了。
注意：when while as after before as soon as since till /until by the time 在時間狀語從句中，要注意時態一致。一般情況下主句是將來時的時候，從句要用一般現在時。
六、練習：在下列各句的空格中填入適當的連詞
1._____ he comes tomorrow, I shall ask where he has been.
2._____ he was speaking, everybody listened carefully.
3.I saw her just _____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. It was not _____ he took off his eyeglasses that I recognized him.
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. We played outside till sunset, ______it began to rain。
20. _______ I get to the airport, I will phone you to pick me up.
21. They were about to leave _____ it began to rain.
22. He always stay in bed _____ lunch time.
23. I like playing tennis _______my younger sister prefers watching ball games.
24. ______ I understand your viewpoint, I don’t agree with you.
25. ______ she grew older, she became more responsible.
二、從A、B、C、D中選出可以填入空白處的最佳答案。
1. It was quiet _____those big trucks started coming through the town.
A. before B. after C. until D. unless
2. It seemed only seconds _____ the boy finished washing his face.
A. when B. before C. after D. even if
3. Hardly had he reached the school gate _____ the bell rang.
A. while B. when C. as D. as soon as
4. ______you begin, I think you must continue.
A. When B. Whenever C. Once D. Even if
5. I remembered you ______ I saw you at the airport.
A. the moment B. while C. after D. once
6. He was about to go to bed ______ the doorbell rang.
A. while B. as C. before D. when
7.______I listen to your advice, I get into trouble.
A. Every time B. When C. While D. Until
8. _____ John was watching TV, his wife was cooking.
A. As B. As soon as C. While D. Till
9. The children ran away from the orchard(果園) ______ they saw the guard.
A. the moment B. after C. before D. as
Key:
1. When 2. While / When 3. as 4. when/as 5. when
6. when 7. when 8. while 9. while 10. whenever 11. before
12. After 13. since 14. till/until 15. until 16. before
17. as soon as 18. before 19. when 20. As soon as 21.when
22. until 23. while 24. While 25. As
二、1. C 2. B 3. B 4. C 5. A 6. D 7.A 8.C 9.A
一、when 的用法
如果只從現象來看，when 從句用的最多的是一般過去時，而主句的時態沒有限制,根據具體情況而定。
1. When he was a child he was always trying out new ideas.他小時候就常常試驗一些新的設想。
2. When she came into my room, I was just reading a book. 她走進我房間時，我正在看書。
3. Were you writing when the teacher came in? 老師進來的時候，你在寫信嗎?
4. Sorry, I was out when you called me. 對不起，你打電話來的時候我出去了。
5. He was on the point of leaving when someone knocked at the door.他正要走，這時有人敲門。
6. I thought of it just when you opened your mouth. 就在你要說話的時候，我也想到了。
7. I had hardly[scarcely] closed my eyes when someone knocked at the door.我剛一閉上眼，就有人在敲門了。
根據以上的例句，我們可以總結出一點：when 從句的A事件，相當於另一個事件B發生的時間點。也就是說，when 從句的重點不在動作本身發生的狀態，而只是把它作為一個時間點，所以when 多數情況下用的是一般過去時，則不用正在進行時。因為如果用正在進行時，它表示的就是一段時間而不是一個時間點了。根據這一點，有的文章補充說：when 從句的動詞大多是瞬時動詞。這種說法也可以參照。
實際上，when 從句也可以有其它的時態，但幾乎也不用進行時，因為它也只是作為一個時間參照點。例如：
1. When I got to the airport, the guests had left. 當我趕到飛機場時，客人們已經離開了。
2. When he had finished his homework, he took a short rest.當他完成作業後，他休息了一會兒。
3. Why do you want a new job when you have got such a good one already?你已經找到如此好的工作，為何還想再找新的?
4. You shall borrow the book when I have finished reading it.在我讀完這本書後，你可以借閱。
5. When the manager comes here for a visit next week, I’ll talk with him about this.下周，經理來這參觀時，我會和他談談此事。
二、while 的用法
相比於when 來說，while 從句的側重點就不一樣了。while 從句的側重點在於描述動作正在發生的狀態，它的意思是：當while 事件正在發生的時候，另一件事如何如何。所以，while 從句一般用的是正在進行時。而另一件事的狀態沒有硬性的要求，根據具體情況而定。例如：
1. While my wife was reading the newspaper, I was watching TV.當妻子正在看報紙的時候，我正在看電視。
2. While Jim was mending his bike, Lin Tao came to see him.正當吉姆修自行車時，林濤來看他。
3. While they were talking, the bell rang. 正在他們談話的時候，上課鈴響了。
4. You can’t do your homework while you’re watching TV.你不能一邊看電視一邊做家庭作業。
5. While John was sitting biting his nails, I was working out a plan to get us home.約翰坐在那裡咬指甲時，我正在制定一個回家的計劃。
從時間的角度來看，while 表示的是一段時間，是一個過程。這是while 的側重點。因此，如果含有“一段時間”的含義的時候，就可以用while。
6. Strike while the iron is hot. 趁熱打鐵。
這句話中，是說趁著鐵是熱的這段時間，趕緊打鐵。如果換成 when 意思就變了，相當於說鐵只熱了一下，打一下，然後鐵就冷了。這顯然不符合文意。
再例：
—I'm going to the post office.
—While you're there, can you get me some stamps?
三、as 的用法
as 從句表示的也是一件事情正在發生，另一件事也正在進行當中。但與 while 從句不同的是，as 從句用的一般不用正在進行時，而只是一般過去時。as 從句一般可以翻譯成“邊……邊……”。例如：
1. As my mother sang those old songs, tears ran down her cheeks.當我媽媽唱起那些老歌時，眼淚順著她的臉頰流了下來。
2. The students took notes as they listened. 學生們邊聽課邊做筆記。
3. As we talked >我們繼續往下談的時候，他越來越興奮。
4. The little girls sang as they went. 小姑娘們一邊走，一邊唱。
5. Just as he caught the ball, there was a tearing sound.當他抓住球的時候，有一種撕裂的聲音。
as 表達的事件，往往只是主句動作發生的背景或條件時，as 只是一個次要的時間說明，不像while 從句有強調 while 動作本身的意思。因此，as 常常翻譯成“隨著……”之意。
例如：
1. As the time went >，the weather got worse. 隨著時間的推移，氣候更加糟糕。
2. The atmosphere gets thinner and thinner as the height increases.隨著高度的增加，大氣越來越稀薄。
3. As years go by，China is getting stronger and richer.隨著時間一年一年過去，中國變得越來越富強了。
少數情況下，如果強調動作正在發生，as 從句也可以用正在進行時。這只能算是特例了。
1. The sad mother sat on the roadside, shouting as she was crying.傷心的媽媽坐在路邊，邊哭邊叫喊。
2. As we were going out, it began to snow. 正當我們出門時，雪開始下起來。
3. He came in as I was going to bed. 我正要上床睡覺，他進來了。
四、when, while, as 的互換
如果從句動作和主句動作同時發生，並且從句動作為延續性動詞時，when，while，as 可以互換使用。
1. When /While /As we were dancing, a stranger came in. 當我們跳舞時，一位陌生人走了進來。[dance 為延續性動詞]
2. When /While /As she was making a phone call, I was writing a letter.當她在打電話時，我正在寫信。[make為延續性動詞]
3. While/When/ As I was walking down the street, I noticed a police car in front of thebank.我順著馬路往前走時，發現銀行門前停著一輛警車。
五、比較while, when, as
1)as, when 引導短暫性動作的動詞。
例如：Just as / Just when / When I stopped my car, a man came up to me.我剎車後，有一個人向我走來。
2)當從句的動作發生於主句動作之前，只能用when 引導這個從句，不可用as 或 while。
例如：When you have finished your work, you may have a rest.幹完活後，你可以休息一下。
3)從句表示“隨時間推移”連詞能用as，不用when 或while。例如：As the day went > 日子一天天過去，天氣越變越壞。
(二)before和after引導的時間狀語從句
Before是主句動作發生在從句的前面。注意before引導的從句不再用否定式的謂語，並且當before引導的從句位於主句之後，有時譯成“就，才”。還要注意主句和從句之間的時間關係。當主句用將來時，從句總是用現在時;如果before引導的從句謂語用的是過去時，則主句動詞多用過去完成時，這樣以便體現動作發生的先後。
After表示主句動作發生在從句動作之後。主句和從句的動作的時間關係正好與before引導的從句相反。例如：
It will be four days before they come back. 他們要過四天才能回來。
Einstein almost knocked me down before he saw me.愛因斯坦幾乎把我撞倒才看到我。
My father had left for Canada just before the letter arrived.我父親恰好在信到之前去加拿大了。
They had not been married four months before they were divorced. 他們結婚還不到四個月就離婚了。
After you think it over, please let me know what you decide.你仔細考慮過以後，告訴我你是怎樣決定的。
After we had finished the work, we went home.完成工作之後，我們回家了。(從句用過去完成時，主句用一般過去時)
(三)比較until和till 的用法
此兩個連詞意義相同。肯定形式表示的意思是“做某事直至某時”，動詞必須是延續性的。否定形式表達的意思是“直至某時才做某事”。動詞為延續性或非延續性都可以。正確使用這兩個連詞的關鍵之一就在於判斷句中的動詞該用肯定式還是否定式。
肯定句：I slept until midnight. 我一直睡到半夜時醒了。
Wait till I call you. 等著我叫你。(在肯定句中可用before代替。
例如
：Let's get in the wheat before the sun sets.)
否定句：She didn't arrive until 6 o'clock. 她直到6點才到。
Don't get off the bus until it has stopped. 公共汽車停穩後再下車。
I didn't manage to do it until you had explained how. 直到你教我後，我才會做。
區別：1)until可用於句首，而till通常不用於句首。
例如：Until you told me, I had heard nothing of what happened. 直到你告訴我以前，出了什麼事我一點也不知道。
2)until when 疑問句中，until要放在句首。
例如：
---Until when are you staying?
你呆到什麼時候?
--- Until next Monday. 呆到下周一。
注意：否定句可用另外兩種句式表示。
3)Not until…在句首，主句用倒裝。
例如：
Not until the early years of the 19th century did man know what heat is. 直到19 世紀初，人類才知道熱為何物。
Not until I began to work did I realize how much time I had wasted. 直到工作，才認識到我已蹉跎了許多歲月。
4)It is not until… that….
例如：It was not until I began to work that I realized how much time I had wasted.
(四)巧辨before和until
在日常英語教學中，我們遇到學生問這樣的一些問題：
1.He will spend six hours at his desk____he finishes his composition.
A.before B.until C.after D.when
2.The bike hit the tree____I could get off.
A.when B.before C.while D.until
3.I knocked at the door for more than five minutes____Mrs white answered it.
A.until B.when C.after D.before
4.It was____yesterday____be____the secret.
A.not until;that;knew B.until;when;knew
C.not before;that;found D.before;that;didn't find
怎樣才能清楚地解釋其選擇的原因，這就涉及到until與before的區別問題。
實際上，只要我們把握住兩者使用時本身的含義及主句動詞是終止性的，還是延續性的，肯定式，還是否定式兩大點，就能容易地解決這類問題。現詳細闡明如下：
一、在下列情況下，兩者可互換用，但含義略有不同
before表示“在……之前”的意思，強調時間先後關係;而until表示“直到……才”的意思，主句是肯定句則表示主句動作的終止時間;主句是否定句則強調主句動作的起始時間。
1.主句為否定式終止性謂語動詞。常見的動詞是open,start,leave,arrive,finish, stop等。例如：
(1)The noise of the street didn't stop until/before it was midnight.
(2)The children won't come back until/before it is dark.
(3)I didn't leave the lovely boy until/before his mother came home.
2.主句為肯定式、延續性謂語詞，這類動詞用stand,stay,talk,be,wait等。例如：
(1)He lived with his parents until/before he graduated from school.
(2)I will wait until/before he comes to my help.
(3)I shall stay heer until/before you come back.
二、在下列情況下，用before不用until
1.主句這肯定式、終止性謂語動詞，只用before。例：
(1)He fell asleep before I could take off his clothes.
(2)We arrived there before it atarted to rain.
(3)The holiday came to the end befor I knew it.
(4)He almost knocked me down before he saw me.
2.主句謂語動詞強調動詞的遲緩性，只用before，常伴有時間段狀語或時間段暗示。例：
(1)It was quite some time before he found the elephant at all.
(2)We had walked a long way before we found some water.
(3)We had sailed for two days before we saw the land.
(4)The fire lasted about four hours before the firefighters could
countrol it.
(5)It was midnight before my brother came home.
(6)It was three months before they met again.
3.如果強調從句謂語動作未發生，就發生主句謂語動作，只用before。常譯為“未及”，“不”或“不等……就”。例：
(1)We can leave early in the morning before it gets too hot.
(2)I must write it down before I forget it.
(3)We do want to buy something now before prices go up.
4.表“與其說……倒不如”，“與其……毋寧……”只用before。例：
(1)I would give up my job before I'd agree to be dismissed.
(2)He will die of hunger before he will steal.
5.在某些特定句型中用before。例如：
(1)It was not long before the whole country rose up.
(2)It will probably not be long before they understand each other.
三、下列情況一般區別用until
1.主句是持續性謂語動詞時，肯定、否定都可以，但意義完全不同。肯定表動作終止，而否定表動作開始。例如：
(1)We discussed the problem until/before he came back.我們一直討論到他回 來。
(2)We didn't discuss the problem until he came back.我們一直等到他回來後才討論問題。
2.not…until句型儘管在某些情況下可與before互換用，但在強調句中一般仍用until。
例如：
(1)It was not until he told me that I knew it.
(2)It was not until he finished his homework that he went home.
綜上所述，前面的4條選擇題中，第1、3題強調動作發生的遲緩性應選before。第2題表動作未及發生就發生主句動作也應選before。第4題為強調句應選A項。
(五)其他時間狀語從句的用法
1.由since引導的時間狀語從句。
since引導的從句的謂語動詞可以是延續性的動詞，又可以是瞬時動詞。一般情況下，從句謂語動詞用一般過去時，而主句的謂語動詞用現在完成時。但在It is +時間+since從句的句型中，主句多用一般現在時。例如：
I have been in Beijing since you left. 自從你離開以來，我一直在北京了。
Where have you been since I last saw you? 自上次我和你見面以後，你到哪裡去了?
It is four years since my sister lived in Beijing. 我妹妹不在北京住有四年了。
It is five months since our boss was in Beijing.我們老闆離開北京有五個月了。
知識擴展
1. It is since從。。。以來多長時間了(因為since +從句或名詞，表示一段時間)
It is five years since we met last time.從我們上次見面已經五年了。
2. It is +before…(。。。才)It was a long time before I went to sleep again.過了很長時間我才睡著。It was an hour before(=until) the police arrived.過了一個小時，警察才來。
3.由as soon as, immediately, directly, instantly, the moment, the instant, the minute, 等引導的時間狀語從句。這些連詞都表示“一……就”。
例如：I will go there directly I have finished my breakfast. 吃完早飯，我立即到那裡去。
The moment I heard the news, I hastened to the spot.我一聽到消息，馬上趕到了出事地點。
As soon as I reach Canada, I will ring you up. 我一到加拿大，就給你來電話。
4.由by the time引導的時間狀語從句。注意時態的變化：在一般情況下，如果從句的謂語動詞用一般過去時，主句的謂語動詞用過去完成時;如果主句的謂語動詞用一般現在時，主句的謂語動詞用將來完成時。
例如：By the time you came back, I had finished this book.到你回來時，我已經寫完這本書了。
By the time you come here tomorrow, I will have finished this work. 你明天來這兒的時候，我將已經完成此工作了。
注意：when while as after before as soon as since till /until by the time 在時間狀語從句中，要注意時態一致。一般情況下主句是將來時的時候，從句要用一般現在時。
六、練習：在下列各句的空格中填入適當的連詞
1._____ he comes tomorrow, I shall ask where he has been.
2._____ he was speaking, everybody listened carefully.
3.I saw her just _____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. It was not _____ he took off his eyeglasses that I recognized him.
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. We played outside till sunset, ______it began to rain。
20. _______ I get to the airport, I will phone you to pick me up.
21. They were about to leave _____ it began to rain.
22. He always stay in bed _____ lunch time.
23. I like playing tennis _______my younger sister prefers watching ball games.
24. ______ I understand your viewpoint, I don’t agree with you.
25. ______ she grew older, she became more responsible.
二、從A、B、C、D中選出可以填入空白處的最佳答案。
1. It was quiet _____those big trucks started coming through the town.
A. before B. after C. until D. unless
2. It seemed only seconds _____ the boy finished washing his face.
A. when B. before C. after D. even if
3. Hardly had he reached the school gate _____ the bell rang.
A. while B. when C. as D. as soon as
4. ______you begin, I think you must continue.
A. When B. Whenever C. Once D. Even if
5. I remembered you ______ I saw you at the airport.
A. the moment B. while C. after D. once
6. He was about to go to bed ______ the doorbell rang.
A. while B. as C. before D. when
7.______I listen to your advice, I get into trouble.
A. Every time B. When C. While D. Until
8. _____ John was watching TV, his wife was cooking.
A. As B. As soon as C. While D. Till
9. The children ran away from the orchard(果園) ______ they saw the guard.
A. the moment B. after C. before D. as
Key:
1. When 2. While / When 3. as 4. when/as 5. when
6. when 7. when 8. while 9. while 10. whenever 11. before
12. After 13. since 14. till/until 15. until 16. before
17. as soon as 18. before 19. when 20. As soon as 21.when
22. until 23. while 24. While 25. As
二、1. C 2. B 3. B 4. C 5. A 6. D 7.A 8.C 9.A
收藏