在英语语法中，过去完成时是用来描述已经完成的动作或事件，通常表示过去的某个时间点之前已经发生的事情。在使用过去完成时时，我们需要注意使用一些固定的句型表达。
一、用于描述过去完成时的时间状语
- By the time (到...时为止)
例如：By the time I arrived, they had already left. (我到达时，他们已经离开了。)
- Before (在...之前)
例如：Before I left, I had finished my homework. (在我离开之前，我已经完成了我的作业。)
- After (在...之后)
例如：After I had eaten breakfast, I went to work. (在我吃完早餐后，我去上班了。)
二、用于描述过去完成时的动作/事件
- Had + 过去分词
例如：I had already finished my work when he called me. (当他给我打电话时，我已经完成了我的工作。)
- Had been + 现在分词
例如：I had been waiting for him for an hour before he finally arrived. (他最终到达之前，我已经等了一个小时了。)
- Had not + 过去分词
例如：I had not seen her before yesterday. (直到昨天我才见到她。)
以上是过去完成时的固定句型表达，我们在使用时需要根据具体的语境进行灵活运用。希望本文对大家有所帮助！
