while, as, when用法区别

while, as, when的用法及区别,很多同学还是没有搞懂,今天给大家简单说明一下:

三者都可以引导时间状语从句,表示主句动作发生的背景。例如:

When/ As/ While we were still laughing, the teacher came in.

区别:

1) when 既可以引导一持续性动作,又可引导一短暂性动作;它可以表示主句的动作和从句的动作同时发生,或从句的动作发生在主句的动作之前。例如:

When I was a boy, I used to go to the seashore on Sundays. (同时)

When you have finished your work, you may have a rest. (从句动作发生在主句动作之前)

2) as引导一持续性动作,侧重于表示主句和从句的动同时发生,但持续时间一般较短。例如:

John sang as he worked.

从句表示“随时间推移”,也只能用as。例如:

As the day went on, the weather got worse. 日子一天天过去,天气越变越坏。

3) while所引导的从句谓语必须是延续性动词,含义相当于during the time that。它也强调主句动作和从句动作的同时发生,往往侧重于主句动作和从句动作的对比。例如:

Please don’t talk so loud while others are working.

While John was reading, I was watching TV.

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