2015年卫生类职称英语考试语法知识：before和after引导的时间状语从句

由before和after引导的时间状语从句。

注意before引导的从句不再用否定式的谓语，主句用将来时，从句总是用现在时;如果before引导的从句谓语用的是过去时，则主句动词多用过去完成时或者一般过去时，根据情况可翻译成“...才....”，“....就....”，“....还没....”，“...趁着....”“然后...." 等。After表示主句动作发生在从句动作之后。主句和从句的动作的时间关系正好与before引导的从句相反。例如：

It will be four days before they come back. (...才....)

It wasn't long before they got arrested by the policemen.(就)

Einstein almost knocked me down before he saw me.(才)

My father had left for Canada just before the letter arrived.(才)

They had not been married four months before they were divorced.(就)

Think before you leap.(然后)

He had gone out of the door before I could say a single word of it.(还没)

Do it before it gets worse.(趁着)

Eat it before the food gets cold.(趁着)

Don't let me know what you decide beforeyou think it over.

After you think it over, please let me know what you decide.

After we had finished the work, we went home.(从句用过去完成时，主句用一般过去时)