as和when有什么区别?

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as和when有什么区别?as和when有什么区别?as和when有什么区别?as和when均可用作从属连词,引导时间状语从句,作“当……时候”解.它们所引导的时间状语从句有时意思一样,有时却有差异.

as和when有什么区别?
as和when有什么区别?

as和when有什么区别?
as和when均可用作从属连词,引导时间状语从句,作“当……时候”解.它们所引导的时间状语从句有时意思一样,有时却有差异.意思相同时,可以互换使用;意思不同时,则不能互换.
as的意思是“正当……时候(just as,at the same moment that)”“随着……(while,when)”,它既可表示一个具体的时间点,也可以表示一段时间.as可表示主句和从句的动作同时发生或同时持续,即“点点重合”“线线重合”;又可表示一个动作发生在另一个动作的持续过程中,即“点线重合”,但不能表示两个动作一前一后发生.如果主句和从句的谓语动词都表示持续性的动作,二者均可用进行时,也可以一个用进行时,一个用一般时或者都用一般时.例如:
1.As I got on the bus,he got off.
我上车,他下车.(点点重合)
2.He was writing as I was reading.
我看书时,他在写字.(线线重合)
3.The students were talking as the teacher came in.
老师进来时,学生们正在讲话.(点线重合)
when的意思是“当……时候(at the time that)”“无论什么时候(whenever)” “一……就……(as soon as )” “在……以后(after)”.它表示的时间概念比较广泛,上述例句中的as或while均可用when代替,因为when不但可以表示具体的时间点,而且也可以表示一段时间.在时间上它既能表示“点点重合”“线线重合”,又能表示“点线重合”.例如:
1.When he came in,she went out.
他进来,她出去.(点点重合)
此句中when从句的动作表示的是一个时间点,when可以用as代替,但不能用while代替.
2.When he came back,I was doing some washing.
他回来时,我在洗衣服.(点线重合)
此句中when从句的动作表示的是一个时间点,所以只能用as代替,不能用while代替.
3.When Mary was writing a letter,the children were playing outside.
玛丽写信时,孩子们都在外面玩.(线线重合)
此句中的when从句的动作表示的是一段时间,可以用用as代替.

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...

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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

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