时间状语从句
时间状语从句常用的连词有：when,as,while,before,after,since,till,until,as soon as,once.
【例】
Before I could get in a word,he already gave orders.
我还来不及插话,他已经吩咐下去了.
After the students were all in the lab,the professor brought out three bottles.
在学生们全进入实验室后,教授拿出三个瓶子来.
学习时间状语从句应注意以下几点：
（1）时间状语从句中一般不使用将来时态,尽管主句使用将来时态,一般使用一般现在时态或现在完成时态.
【例】
I'll go on with the work when I come back tomorrow.
我明天回来,我将继续做这项工作.
Please tell him about it when you see him back.
你看到他回来,就告诉他这件事.
（2）till/until引导时间状语从句,主句的谓语动词如是延续动词,可使用否定或不用否定,如果是不延续动词,必须使用否定形式.
【例】
He didn't go to bed until it was 12 o'clock last night.
他昨晚十二点才上床睡觉.
They worked until it was dark.
他们一直工作到天黑.
（3）as soon as,the moment,every time,each time,the minute,the instant,the day,the week,the year,the first time,next time,any time,the last time,all the time,from the time,by the time,immediately,instantly,directly等表示时间的词语,后面也可以接时间状语从句,表示“一……就……”.
【例】
I recognized you the minute I saw you.
我一见到你,就认出了你.
By the time he was fourteen,he had built his own lab.
到他十四岁的时候,他已建起自己的实验室.
（4）主句使用过去进行时或过去完成时,或是was/were about to do Sth.,后面从句使用when从句,而且谓语动词使用一般过去时,这时when不当“当……时候”解,而当“突然”解.
【例】
They were working in the fields when it began to rain.
他们在地里正干着活时,天突然下起雨来.
He was about to leave when the telephone rang.
他刚要走,突然电话铃响了.