引導時間狀語從句
1.表示“當……的時候”，相當于at the moment when。
（1）When we got to the cinema,the film had been on for half an hour.當我們到電影院時，電影已經放映半小時了。
（2）She was writing a letter when I came in.當我進來時，她在寫信。
2.表示“一……就……”，相當于as soon as。
（1）The students got up when the bell rang.鈴聲一響，學生們就起床了。
（2）I’ll ring you up when I arrive in Beijing.我一到北京就給你打電話。
3.表示“就在這時；當時”，相當于just at the moment或just then。
（1）We were about to start out when it began to rain heavily.我們正要啟程，就在這，天下起了大雨。
（2）He had just returned from one business trip when he was asked to make another one.他剛剛出差回來，這時，又叫他再次出差。
4.表示“每當；每次”，相當于every time或whenever。
（1）She always turns to us for help when she is in trouble.每當她遇到困難，她總是向我們求助。
（2）It is freezing cold here when it snows.每當這兒下雪，天氣就十分寒冷。
5.表示“當……之后”，相當于after the time that。
（1）We went home when the film was over.電影結束以后，我們回家去了。
（2）When she got home，she started to prepare supper.她回到家后，開始準備晚飯。