.时间状语： 比较while, when, as考试重点

1)as, when 引导短暂性动作的动词。

Just as / Just when / When I stopped my car, a man came up to me.

2)当从句的动作发生于主句动作之前，只能用when 引导这个从句，不可用as 或 while。

When you have finished your work, you may have a rest.

3)从句表示"随时间推移"连词能用as，不用when 或while。

As the day went on, the weather goes warm.

4)while只能跟延续性动词，when既可跟延续性的又可跟不能延续性的动词，所以有时通用。

When I got home, my mother was cooking. While my mother was cooking, I got home.