While when as 中as怎么用，什么时候用，与其他两个有什么区别.

Question

如题所述

Answer 1

when,while,as引导时间状语从句的区别
when,while,as显然都可以引导时间状语从句,但用法区别非常大.
一、when可以和延续性动词连用,也可以和短暂性动词连用；而while和as只能和延续性动词连用.
① Why do you want a new job when youve got such a good one already?（get为短暂性动词）你已经找到如此好的工作,为何还想再找新的?
②Sorry,I was out when you called me．（call为短暂性动词）对不起,你打电话时我刚好外出了.
③Strike while the iron is hot．（is为延续性动词,表示一种持续的状态）趁热打铁.
④ The students took notes as they listened．（listen为延续性动词）学生们边听课边做笔记.
二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生；while和as从句的谓语动作必须是和主句谓语动作同时发生.
1．从句动作在主句动作前发生,只用 when.
①When he had finished his homework,he took a short rest．（finished先发生）当他完成作业后,他休息了一会儿.
②When I got to the airport,the guests had left．（got to后发生）当我赶到飞机场时,客人们已经离开了.
2．从句动作和主句动作同时发生,且从句动作为延续性动词时,when,while,as都可使用.
①When ／While ／As we were dancing,a stranger came in．（dance为延续性动词）当我们跳舞时,一位陌生人走了进来.
②When ／While ／As she was making a phonecall,I was writing a letter．（make为延续性动词）当她在打电话时,我正在写信.
3．当主句、从句动作同时进行,从句动作的时间概念淡化,而主要表示主句动作发生的背景或条件时,只能用 as.这时,as常表示“随着……”；“一边……,一边……”之意.
① As the time went on,the weather got worse．（as表示“随着……”之意）
② The atmosphere gets thinner and thinner as the height increases．随着高度的增加,大气越来越稀薄.
③As years go by,China is getting stronger and richer．随着时间一年一年过去,中国变得越来越富强了.
④The little girls sang as they went．小姑娘们一边走,一边唱.
⑤The sad mother sat on the roadside,shouting as she was crying．伤心的妈妈坐在路边,边哭边叫.
4．在将来时从句中,常用when,且从句须用一般时代替将来时.
①You shall borrow the book when I have finished reading it．在我读完这本书后,你可以借阅.
②When the manager comes here for a visit next week,Ill talk with him about this．下周,经理来这参观时,我会和他谈谈此事.
三、when用于表示“一……就……”的句型中（指过去的事情）.
sb．had hardly（＝scarcely） done sth．when．．．＝Hardly ／ Scarcely had sb．done sth．when．．．
①I had hardly ／scarcely closed my eyes when someone knocked at the door．＝Hardly ／ Scarcely had I closed my eyes when someone knocked at the door．我刚一闭上眼,就有人在敲门了.
②I had hardly ／scarcely entered my room when the telephone rang．＝Hardly ／Scarcely had I entered my room when the telephone rang．我刚一走进房门,电话就响了。

Answer 2

while 后面接延续性行为,但这个动作肯定和主句动作时间不一样长.如：he was talking to me while he was watching the tv.应该说“看电视”比“谈话”时间长.而as通常两个动作一直相随,很可能时间相同.如：he was thinking of a question as watching the tv.这两个动作就是一直相随的.
as意为“一边……一边……”或“与……同时”,重在表示动作同时发生、伴随进行.while只指“时间段”,不指“时间点”,从句的动词只限于持续性动词.
1 从句表示"随时间推移"连词能用as,不用while.
As the day went on,the weather got worse.
日子一天天过去,天气越变越坏.
2 as引导短暂性动作的动词.
Just as I stopped my car,a man came up to me.
————————————————————————————————
when,as,while用法之异同
请看99年高考的一个选择题：
－I′m going to the post office.
－_____ you are there,can you buy me some stamps?
A．As B．while C．Because D．If
根据本题语境,选项C、D显然不合题意,故答案应在A、B之间选择.为什么正确答案为B而不是A呢?
先看when,as,while在引导时间状语从句时的主要用法：
when表示“当……的时候”.从句中既可用延续性动词,又可用非延续性动词,这些动词既可以表示动作,又可表示状态.从句中的动作既可和主句的动作同时发生,又可在主句的动作之前或之后发生.如：
When I came into the room,I found him lying there asleep.
Mary was having dinner when I saw her.
When you meet a word you don't know,consult the dictionary.
She was beautiful when she was a girl.
如果when从句的主语与主句主语相同,谓语又是be动词,从句主语和be可以省略：当when从句主语与主句主语相同时,用when加分词可以替代状语从句.如：
When（you are）in trouble,ask her for help.
When（I was）sleeping,I never heard a thing.
as表示"当……时""一面……一面","随着".其具体用法如下：
1、表示"当……时"、"和……同时".常指从句的动作未结束,主句中的动作就已发生.从句中多用表示动作的动词,而不用be动词或表示感觉、理解、知道这类动词.
As he stood there,he saw two men enter the bar.
She dropped the glass as she stood up.
As I was walking down the street,an American asked me for directions to the nearest station.
2、用于平行的动作中,表示"一面……一面……".常指一个主语同时进行两个动作.如：
He sang as he worked.
The students took notes as they listened.
3、用于平行发展的结构中,表示"随着……".常指一个行为是另一个行为的结果,或一种状态随另一种状态变化.句中的动词多表示状态的发展变化.
As the wind rose the noise increased.
As it grew darker it became colder.
As he grew older he became more confident.
While表示"在……的时候"、"在……期间".它强调主句的动作与从句的动作同时发生或主句的动作发生在从句的动作过程中.While从句中必须是表示动作或状态的延续性动词.如：
Never get on or off a bus while it is in motion.
The weather was fine while we were in Beijing.
She called while I was out.
1、如果主句的动作在从句的动作过程中发生,从句常用进行时.如：
While we were swimming someone stole our clothes.
Don′t talk so loud while others are working.

2、如果主句和从句主语相同,while加现在分词可代替状语从句.如：

We must strike while the iron is hot.

He took a bath while I was preparing dinner.

Come and pay a visit to the park while the flowers are in bloom.

通过以上分析我们可以看出,when,as,while引导时间状语从句时,侧重点有所不同.

1、When可指时间点,又可指时间段,从句中可用延续性动词,也可用非延续性动词.

2、While总是指一个时间段,从句中必须用延续性动词.

3、as多用于平行结构.表示两个动作同时发生：一个主语同时进行两个动作：一种状态随另一种状态的变化而变化.

4、表示主句的动作发生在从句的较长动作过程中,when,while,as均可使用.从句中为be动词时,多用when和while.谈论两个同时进行的长动作可用while；谈论两个平行动作或两种状态变化多用as.
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Answer 3

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