1．时间状语从句注意点

___________l 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表示从句动作和主句动作同时发生，或先于主句动作； while表示从句的动作与主句动作同时发生，并有延续的含义； as从句动作与主句动作相并发生，常译为“边…边…” 。

When/While

When

While

as

1) when／while／as的用法。