表示动作或状态从过去的某一时间以前开始并一直延续到这一时间，常与延续性动词连用。例如 I had stayed in beijing for three days by then.表示动作在过去某一时间之前已经结束。与非延续性动词连用。例如when they got to the field, the football match had already started.表示过去某一时间以前反复发生的动作或出现的状态。例如He said he had read the detective novel twice.表示过去未实现的的愿望或意图。例如I had hope to be able to take my seat.
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