1．时间状语从句注意点

___________ I was walking down the street，I saw some policemen． _______they heard the news，they were surprised． ______the child was playing with his toys，his parents were watching TV. They shouted slogans ____they passed the square.

when即可引导一个持续动作, 也可引导一个短暂动作, 表示从句动作和主句动作同时发生，或先于主句动作； while只能引导一个持续动作,表示从句的动作与主句动作同时发生. as从句动作与主句动作相并发生，常译为“边……” 。

When/While

When

While

as

1) when／while／as的用法: