过去完成时表示过去某一时间以前发生的动作或存在的状态。这个“过去的某一时间”可以用某些时间状语表示，也可以通过语境来体现。

2.When I reached the station, the train had left.

the Past Perfect Tense:

had done

※ 图示：

  过去 现在 将来

_____________________│__________________

│ │

past perfect simple past

Eg:1. We had had supper by 6:00 pm that day.