什么是过去完成时？
过去完成时是一种相对时态，即以某一过去吋间作参照，过去完成时表示的动作发生在这一过去时间之前，所以我们可以简单地用"过去的过去"这五个字来理解过去完成吋态。如：
1. He______more than 5000 English words when he entered the university at the age of 15.
A. has learned B. would have learned C. learned D. had learned
【分析】答案选D。因为上大学是过去，学了五千个英语单词是在上大学之前，即"过去的过去"，所以用过去完成吋。
【注】用于某些特殊句型：no sooner''''''than ， hardly''''''when ， scarcely''''''before等。如：
We had no sooner set out than a thunderstorm broke.
我们刚出发就遇到了大雷雨。（主句谓语要用过去完成时）
He had hai'dly arrived when it began to snow. 他一到，天就下起雪来了 。（主句谓语要用过去完成时）
Scarcely had I arrived at the station before the train left.
我剛抵达车站，火车就走了 。（主句谓语要用过去完成时）
2.When the old man______to walk back to his house ， the sun______itself behind the mountain.
A. started;had already hidden B. had started ；had already hidden
C. had started；was hiding D. was starting ；hid
【分析】答案选A。根据句意，"开始回房子"发生在过去，"太阳落山"是在"开始回房子"之前，故过去的过去。
3.Father______for London on business upon my arrival,so I didn't see him.
A. has left B. left C. was leaving D. had left
【分析】答案选D。根据"我没见到他"可知，"在我到达"前"父亲已经去伦敦"了，即父亲去伦敦发生在"过去的过去"，故用过去完成时。
4.The policeman 's attention was suddenly caught by a small box which______placed under the Minister 's car.
A. has been B. was being C. had been D. would be
【分析】答案选C。因为这个小盒子"被放在部长车下"发生在"引起警察注意"之前，即"过去的过去"，所以用过去完成时。
5." Hurry up ！ Alice and Sue are waiting for you at the school gate. " " Oh ！ I______thought they without me."
A. wen B. are going C. have gone D. had gone
【分析】答案选D。因为thought(原以为）用的是过去时，所以他们"走了"就是"过去的过去"，故用过去完成时。