Adverbial clausesof time / reason（时间、原因状语从句）
Adverbial clause of time:
when, while, asbefore, aftersince, till/until, by the timeas soon as = the moment hardly…when = no sooner…thanthe first time, every/each timewhenever等
when (特定时间或一段时间)① 当…时侯----When I was a boy, I rode to school. ----When the lesson was over, we walked out of the lab. ② 就在那时 ----I was doing my homework when the light suddenly went off.----He was about to sleep when someone knocked at the door.
when / while / as区分
过去进行时
过去 ...