1.过去完成时的构成
过去完成时由had 过去分词构成，其中had不随人称和数的变化而变化。
I had finished my homework when my father arrived home last night.昨晚我父亲到家时，我已经完成了作业。
They had just had their dinner when I called.我打电话来时，他们刚吃完晚饭。
2.过去完成时的用法
①过去完成时表示在过去的某个动作或时间之前已经发生的动作或已经存在的状态，也称为“过去的过去”。常用的时间状语有：when，before，than，until引导的含有过去时的时间状语从句，by（到...为止）引导的时间状语（例如，by the end of last year到去年末为止）
By the end of last year, we had planted 2000 trees.到去年年末为止，我们已种了2000棵树。
He had known the incident before I toldhim about it.在我告诉他这件事之前，他已经知道了。
When the enemy arrived at the village, our troops had already left.敌人到达村庄时，我们的部队已经离开了。
②过去完成时表示一个动作或状态在过去某一时间之前开始，一直持续到过去这一时间，并有可能持续下去。常用的时间状语有：for 段时间，since 点时间或从句，after引导的时间状语从句。
We were happy to see him because he had been away from us for two years.我们很高兴见到他，因为他已经离开我们两年了。
It was dinner time and he was tired because he had worked since dawn.现在是吃晚饭的时间，他很累，因为他从天亮就开始工作。
③过去完成时表示原有的打算，意图，希望等，但没有实现，常用的动词有：think，want，hope，intend，mean，suppose，expect，plan等。
I had expected to visit the Great Wall last summer, but I didn’t have enough time. 去年夏天我本来想去参观长城，但是我没有足够的时间。
I had hoped to see him, but he left ahead of time.我本来希望见到他，但他提前走了。
④过去完成时用于虚拟语气中，表示与过去事实相反的情况，常用于：if引导的条件句中，wish引导的宾语从句中，as if引导的状语从句中。
If you had come here yesterday, you would have seen the movie star.如果你昨天来这里，你就会看到那个电影明星了。
I wish I had passed the exam last term.我真希望我上学期通过了考试。
He spoke as if he had been to England.他说起话来好像去过英国似的。
⑤过去完成时用于固定句型中：hardly/scarcely/barely...when...; no sooner... than...刚...就，其中主句时态常用过去完成时。
He had hardly arrived home when it began to rain.他刚到家就开始下雨了。
He had no sooner left home than the telephone rang.他刚离开家，电话铃就响了。
当hardly/scarcely/barely/no sooner位于句首时，主句部分倒装。
Hardly had he arrived home when it began to rain.
No sooner had he left home than the telephone rang.
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