Question

when，as，while引导时间状语从句时有什么区别

Answer 1

when 从句用的最多的是一般过去时,而主句的时态没有限制,根据具体情况而定.
(e.g.) Sorry,I was out when you called me.
一般情况下,when 引导时间状语从句的话,从句发生的事件,相当于另一个主句发生的时间点.从句的重点是把它作为一个时间点,所以when 多数情况下用的是一般过去时,则不用正在进行时.when引导时间状语从句,从句也可以有其它的时态,不过也只是作为一个时间参照点,比如过去完成时.基本上没有进行时的句子.
(e.g.) When I got to the airport,the guests had left.
注意把when引导的宾语从句和时间状语从句分开,就看能不能调位置了
(e.g.) I don’t know when he will come tomorrow.
相比于when 来说,while 引导时间状语从句的话,侧重点就不一样了.当while 事件正在发生的时候,另一件事如何如何.所以,一般用的是正在进行时.而另一件事的状态没有硬性的要求,根据具体情况而定.例如：
(e.g.) While we were talking ,the bell rang.
(e.g.) You can’t do your homework while you’re watching TV.
while 表示的是一段时间,是一个过程.如果时间提示词有“一段时间”的含义的时候,选择while.而且while的谓语动词必须是延续性动词,不能是瞬时动词.
as 从句正在发生,主句也正在进行当中.as 从句多数为一般过去时.也可以翻译成咱们常说的“一边……一边……”
(e.g.) The students took notes as they listened．
as 表达的事件,往往只是主句动作发生的背景或条件时,翻译成“随着……”
(e.g.) As the time went on,the weather got worse.随着时间的推移,气候更加糟糕.
如果强调动作正在发生,as 从句也可以用正在进行时.
(e.g.) As we was going out,it began to snow.
希望采纳哦！

Answer 2

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。

when, while这三个词都有"当……时候"之意，但用法有所不同，使用时要特别注意。

①when意为"在……时刻或时期"，它可兼指"时间点"与"时间段"，所引导的从句的动词既可以是终止性动词，也可是持续性动词。如：

When I got home, he was having supper.我到家时，他正在吃饭。

When I was young, I liked dancing.我年轻时喜欢跳舞。

②while只指"时间段"，不指"时间点"，从句的动词只限于持续性动词。如：

While I slept, a thief broke in.在我睡觉时,盗贼闯了进来。
辨析

①when从句与主句动作先后发生时，不能与while互换。如：

When he has finished his work, he takes a short rest.每当他做完工作后，总要稍稍休息一下。(when = after)

When I got to the cinema, the film had already begun.当我到电影院时，电影已经开始了。(when=before)

②when从句动词为终止性动词时，不能由while替换。如：

When he came yesterday, we were playing basketball.昨天他来时，我们正在打篮球。

③当从句的谓语是表动作的延续性动词时，when, while才有可能互相替代。如：

While / When we were still laughing, the teacher came in.正当我们仍在大声嬉笑时，老师进来了。

④当从句的谓语动词是终止性动词，而且主句的谓语动词也是终止性动词时,when可和as通用，而且用as比用when在时间上更为紧凑，有"正当这时"的含义。如：

He came just as (or when) I reached the door.我刚到门那儿，他就来了。

⑤从句的谓语动词如表示状态时，通常用while。如：

We must strike while the iron is hot.我们应该趁热打铁。

⑥while和when都可以用作并列连词。

Mike is tall while his brother is short.迈克的个子很高，然而他弟弟很矮。

Mary was on her way home when two big boys stopped her.玛丽正走在回家的路上，这时两个大个子男孩拦住她。