（1）when, as, while （从属连词） when即可引导持续性动作，又可引导短暂性动作。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动作之前。如： When I was a boy, I used to go to the seashore on Sundays.（同时） When the lesson was over, we began our writing. （从句动作在前）

1、时间状语从句：

引导时间状语从句的从属连词有：when, while, as, whenever, before, after, since, till, until, as soon as, once,the moment, immediately, no sooner…than, hardly…when, by the time, every time, last time…等引导。