2016年职称英语卫生类考试时态之过去完成时：

过去完成时：过去完成时表示过去某一时间或某一动作发生之前已经完成的动作。简言之, 过去完成时所表示的时间是“过去的过去”。

①过去完成时由“助动词had+动词的过去分词”构成。

②过去完成时时间状语有：by (yesterday), by then, by the end of (last…)或者由when,before等引出状语从句。有时句子中会有already, just, once, ever, never等词语,也会有for… 或since…构成的时间状语。如：They had already finished cleaning the classroom when their teacher came.(当老师来的时候他们已经打扫完了教室)/ The woman had left before he realized she was a cheat.(在他发觉那个妇女是个骗子时她已经走掉了)

③过去完成时常用于宾语从句中、after引导的从句中,或者从句是before引导的主句中。如：After I had put on my shoes and hat,I walked into the darkness.(我穿上鞋子戴上帽子走进了黑暗之中)/ He said that he had never seen a kangaroo before.(他说他以前从来没有见过袋鼠)