1．常用来引导时间状语从句的从属连词有：when， whenever，as，while，before, after, since, as soon as等。 (1) when，while和as引导的时间状语从句 ①when“当(在)……时”(=at the time that)可表示瞬间时间； 与主句中谓语动词的动作同步发生，也可有先后。 It was snowing when we got to the airport.(同时发生) 我们到达机场时，天正下着雪。 He went home when he had finished his homework.(先后发生) 做完作业后他回家了。

一、时间状语从句