过去完成时的概念与结构

　概念：表示在过去某一时间或动作之前已经发生或完成了的动作，即“过去的过去（ past-in-the-past ）”。

　　构成：“助动词 had +   过去分词”，其中 had 通用于各种人称。

　　They had already had breakfast before they arrived at the hotel.在到达旅馆之前，他们已经吃过了早饭。

　　She had finished writing the composition by 10：00 this morning. 今天早晨10点之前，她已经写完了作文。