当when和as作“当.时候”时,用法和区别是什么

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当when和as作“当.时候”时,用法和区别是什么

一、when可以和延续性动词连用,也可以和短暂性动词连用;而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.
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;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,as都可使用.
①When /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 /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.