过去完成时
[观察例句]
1．What's more，he had recently received a letter from his father predicting that...
2．After Darwin had spent some time in South America，his room on the ship was crowded with samples of the plants and animals he had collected.
3．At that time，people believed that all species had appeared on Earth at the same time...
4．It seemed their beaks had evolved according to what food was available on that particular island.
[归纳用法]
过去完成时的动作需在过去某一时间之前发生，即发生在“过去的过去”。
1．过去完成时的构成
过去完成时是由“had＋过去分词”构成的。
Soon I realized I had made a serious mistake.
我很快就意识到我犯了一个严重的错误。
The man sitting beside me on the plane was very nervous.He had not flown before.
飞机上坐在我旁边的人很紧张。他以前从没乘过飞机。
2．过去完成时的用法
①“已完成”的用法：
表示某一动作或状态在过去某一时间之前或过去某一动作之前已经完成。句中常用by引导的时间状语或以before，until，when，than等词引导的内含一般过去时的时间状语从句。
By 5：00 yesterday morning we had done that work.
到昨天早上5点钟时，我们已经做完了那件工作。
He had just finished sweeping the classroom when the teacher returned from the office.
老师从办公室回来时，他刚把教室打扫完。
