英语四级考试中，单独考察的题几乎没有，但是语法知识点却贯穿整张试卷，下面是频道为大家整理的知识，希望可以为大家带来帮助，一起来学习一下吧。
　　过去完成时
　　1) 概念：表示过去的过去
　　其构成是had 过去分词构成。
　　那时以前 那时现在
　　2) 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.
　　3)过去完成时的时间状语before, by, until , when, after, once, as soon as。
　　He said that he had learned some English before.
　　By the time he was twelve, Edison had began to make a living by himself.
　　Tom was disappointed that most of the guests had left when he arrived at the party.
　　典型例题
　　The students ___ busily when Miss Brown went to get a book she ___ in the office.
　　A. had written, left
　　B，were writing, has left
　　C. had written, had left
　　D. were writing, had left
　　答案D. "把书忘在办公室"发生在"去取书"这一过去的动作之前，因此"忘了书"这一动作发生在过去的过去，用过去完成时。句中when表示的是时间的一点，表示在"同学们正忙于……"这一背景下，when所引导的动作发生。因此
　　前一句应用过去进行时。
　　注意：
　　had no … when
　　还没等…… 就……
　　had no sooner… than
　　刚…… 就……