表示过去的过去
其构成是had +过去分词.
实际上也就是说在过去已经完成了,Ok了.就是了
附用法：
a. 在told, said, knew, heard, thought等动词后的宾语从句.
She said (that) she had never been to Paris.
b. 状语从句
在过去不同时间发生的两个动作中,发生在先,用过去完成时；发生在后,用一般过去时.
When the police arrived, the thieves had run away.
c. 表示意向的动词,如hope, wish, expect, think, intend, mean, suppose等,用过去完成时表示"原本……,未能……"
We had hoped that you would come, but you didn't.