Unit 5 Revealing nature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。[名师点津]在包含 before 和 after 的复合句中，因为从句动作和主句动作发生的先后顺序已经非常明确，可以用一般过去时代替过去完成时。The train (had) started before I reached the station.在我到达车站之前，列车已经开了。After he (had) arrived in England，Marx worked hard to improve his English.马克思到达英格兰之后，努力提高他的英语水平。②“未完成”的用法：表示一个动作或状态在过去某一时刻之前就已开始，一直持续到这一过去的时间，还可能再持续下去。1Up to that time all had gone well.直到那时一切都很顺利。John and Jane had known each other for a long time before their marriage.约翰和简在结婚前就认识很长时间了。③“想象性...
