过去完成时

1 、过去完成时是一个相对时态，表示过去的过去，只有在两个过去发生的动作相比较时才可显示出来。

e.g. As soon as we got to the station, the train had left.

注：主从句表达的动作紧接时，即两动作发生的时间没有明显时间上的悬殊或空档时，主从句都可用一般过去时。

e.g. Where did your brother study before he joined the army?

2 、过去完成时可表示截止过去某一时间动作的总或动作的结束。

e.g. By the end of last month. We had reviewed four books

By eight o`clock, he had finished his homework.

与这个时态连用的时间状语常有：

by 1985, by eight o`clock, by then, by the end of last month, by the time when, when, as soon as, before 

等连词引导的时间状语从句，表示主句动作结束的时间。