[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。
