过去完成时的基本概念和形式

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过去完成时
过去完成时的基本概念和形式
过去完成时(past perfect tense)表示在过去某一时间或动作以前已经完成了的动作。简言之，过去完成时所表示的时间就是"过去的过去"。过去完成时由助动词had + 过去分词构成。
过去完成时的用法
1)过去完成时表示在过去某一时间或动作以前业已完成的动作。这个过去的时间可以用by，before等介词短语或一个时间状语从句来表示。如：
By the end of last week we had learned ten lessons.到上周末为止，我们已经学了十课书。
He had learned some English before he came to the institute.他来学院之前学过一些英语。
I didn't go to the film because I had seen it twice.我没去看电影，因为这片子我已看过两次了。
When I had gone over my lessons I took a rest.我复习完功课之后，休息了一会儿。
I gave my little sister the flowers that I had bought for her.我把给妹妹买的花送给她。
In the exhibition he saw many oil paintings that he had never seen before.他在展览厅里见到许多过去从未见过的油画。
2)过去完成时可以表示由过去某一时间开始，一直延续到过去另一时间的动作，常和for(有时可以省去)或since构成的短语或since引导的从句连用。如：

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It rained yesterday after it had been dry for many months.在天旱了好几个月之后，昨天下雨了。
By the I read his new book， I had known him for a long time.到我读他的新书时，我早就知道他了。
He said that great Changes had taken place in his hometown since，1980. 他说7980年以来他的家乡大变样了。
[注]当一个由when，before，after，as soon as等连词引导的从句所表示的动作和主句的动作紧接时，两个动作均可用"一般过去时"来表示。如：
We had breakfast after we did morning exercises.做完早操后，我们吃早饭。
When I finished supper，I took a walk.我晚饭后就去散步。
The train started to move just before he reached the platform.他到月台时火车刚开走。
They started ploughing as soon as they got to the fields.他们一到地里就开始耕地。