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。
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?
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。
When 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。
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。
When /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。
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。
As the time went on,the weather got worse.(as表示“随着……”之意)
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
三、when用于表示“一……就……”的句型中(指过去的事情)
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。
追问延续性动词是什么
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