2015年衛(wèi)生類職稱英語考試語法知識：before和after引導的時間狀語從句

由before和after引導的時間狀語從句。

注意before引導的從句不再用否定式的謂語，主句用將來時，從句總是用現(xiàn)在時;如果before引導的從句謂語用的是過去時，則主句動詞多用過去完成時或者一般過去時，根據(jù)情況可翻譯成“...才....”，“....就....”，“....還沒....”，“...趁著....”“然后...." 等。After表示主句動作發(fā)生在從句動作之后。主句和從句的動作的時間關(guān)系正好與before引導的從句相反。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.(還沒)

Do it before it gets worse.(趁著)

Eat it before the food gets cold.(趁著)

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.(從句用過去完成時，主句用一般過去時)