过去完成时的四种：
过去的过去：
By nine o’clock last night, we had got 200 pictures from the spaceship.
由过去的某一时刻开始，一直延续到过去另一时间的动作或状态，常和for, since构成的时间状语连用：
I had been at the bus stop for 20 minutes when a bus finally came.
动词think, want, hope, mean, plan, intend等用过去完成时来表示过去未曾实现的想法，希望，打算或意图等：
They had wanted to help but could not get there in time.
过去完成时还可用在hardly…when…, no sooner…than…, It was the first (second, etc) time (that)…等固定句型中。
Hardly had he begun to speak when the audience interrupted him.
他刚开始演讲，听众就打断了他。
No sooner had he arrived than he went away again.
It was the third time that he had been out of work that year.
通过上的例子和介绍，大家对于SAT语法考试中的难点，过去完成时应该有一个大概的了解了，所以大家在备考自己的SAT语法考试的时候，可以适当的参考和借鉴一下。
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