as.when.while用法有什么区别、具体点、

as.when.while用法有什么区别、具体点、
as.when.while用法有什么区别、具体点、

as.when.while用法有什么区别、具体点、
when,while,as都可以引导时间状语从句,但用法区别非常大.
1.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.
2.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.
3.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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