时间状语从句

　　1)在带有till或until引导的时间状语从句的主从复合句里，如果主句用肯定式，其含义是“一直到……时”，谓语动词只能用延续性动词。如果主句用否定式，其含义是“直到……才……”, “在……以前不……”, 谓语动词可用瞬间动词。例如：

　　The young man read till the light went out.

　　Let’s wait until the rain stops.

　　We won’t start until Bob comes.

　　Don’t get off until the bus stops.

　　2)时间状语从句常用when, as, while, before, after, since, till, until, as soon as等连词来引导。例如：

　　It was raining hard when got to school yesterday.

　　While he was doing his homework, the telephone rang.

　　As he walked along the lake, he sang happily.

　　He had learned a little Chinese before he came to China.

　　After he finished middle school, he went to work in a factory.

　　3)在时间状语从句里，通常不用将来时态，用现在时态表示将来的动作或状态。例如：

　　I’ll ring you up as soon as I get to New York.

　　I will tell him everything when he comes back.

　　He won’t believe it until he sees it with his own eyes.