一、概念过去完成时把时间推移到过去某一时间之前,与现在不发生联系,由“had+-ed分词”构成。它的主要用法有三个,即“已完成用法”,“未完成用法”和“虚拟用法”。已完成用法表示一个动作或状态在过去某一时间或动作之前已经发生或完成。如: First, when the concept was completed in the past, the time was passed before a certain time in the past, and there was no connection with the present. It was composed of “had+-ed word segmentation”. There are three main usages for it, namely “completed usage”, “unfinished usage” and “virtual usage”. Completed usage indicates that an action or state has occurred or completed before a certain time or action. Such as: