as, when, while三个词都有“当……时候”,但是三者的用法确是有很大区别。大家要注意它们的区别,这个知识点也是中考英语的常考知识点,一定要引起重视。
1.as:
①多用于动作发生时间较短时,常有“正当……之时” 之意
He fell off the bike as she got down.
②表“边……边……”或“随着……”之意时常用as
SHe whistled as she rode on.
2.when表示“当……的时候”,引导的从句即可以接延续性动词也可接非延续性动词
When We arrived, it was already midnight.
从句和主句的动作同时发生,但因为从句动作arrived是非延续性的,表示的是“一瞬间”,此时不可用while,但可用as替换。
When the clock struck eleven, all the lights wentout.(从句的动作在主句之前发生)
When he ran to the stop, the bus had gone.(从句动作在主句动作之后发生)
He read a newspaper when he was waiting for a bus.
从句动作和主句动作同时发生,而且从句动作waiting是延续性的,表示的是“一段时间”,此时可用while替换。
3.while:
while意思是during the whole of the time that,指在“一段时间”里,所引导的从句中的动词是延续性的,可译为“在……期间, 在……之时”
She visited a lot of places while she stayed in U.S.
He fell asleep while he was watching TV.
注意:when和 while所能接的动词范围不同
练习:
I was walking onthe street______ a dog ran out.
A. when B. as C. whileD. since
【答案】A