过去完成时的被动语态常用于以下情况：
(1)表示过去某一时间以前已经完成的动作，常与by, before等引导的时间状语连用。
By the time he got to the school, the first period had been finished.
The classroom hadn't been cleaned before the teacher came.
How many buildings had been destroyed when the hurricane ended?
Had the new plan been discussed before the meeting?
(2)在 told, said, knew, heard, thought等动词之后的宾语从句中，若表示过去某一被动动作时，用过去完成时。
The said the production costs had been reduced.
The boy was reminded that his homework had not been handed in.
The media reported more than 1,000 people had been killed in the earthquake.
(3)根据语意可以判断出动作先后的被动语态，用过去完成时。
As the assignment had been done, he went on to search the Internet.
He did what he had been told to
另：当从句由 after，before，when或 as soon as引导时，主句和从句都可以用一般过去时。
When he arrived, he called her.
They locked the door before they left.
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