1. 过去完成时的定义
过去完成时既可表示过去某个时间或动作之前所发生的事情(常用时间状语有already, before, ever, just, never, still, yet)，也可表示过去某个时间或动作之前所发生的动作一直持续到过去某个时间(常接时间状语：since +时间点, for + 时间段)。如：
When I got to the station, the train had left. 当我到达车站时，火车已经开走了。
We had learnt fifteen lessons by last week. 到上周为止，我们学完了十五篇课文。
He had stayed here for two days before he left. 他走之前在这儿呆了两天。
He said that he had lived there since he was ten. 他说他十岁起就住在那儿了。
2. 过去完成时的结构
过去完成时由“had + 过去分词”构成。