在英语语法中，过去完成时是一种用来描述在过去某个时间之前已经完成的动作或状态的时态。它通常用于表达一个动作发生在另一个过去的动作之前。为了帮助大家更好地理解和掌握过去完成时的使用方法，下面是一些练习题及其答案。

练习题

1. By the time I arrived at the station, the train ________ (leave).

2. She had already finished her homework ________ (before/after) she went out.

3. They ________ (not see) each other for five years before they met again.

4. When we got to the restaurant, all the tables ________ (be) taken.

5. He ________ (write) three letters by the time he left home.

答案

1. By the time I arrived at the station, the train had left.

2. She had already finished her homework before she went out.

3. They had not seen each other for five years before they met again.

4. When we got to the restaurant, all the tables were taken.

5. He had written three letters by the time he left home.

通过这些练习题，我们可以看到过去完成时的结构通常是“had + 过去分词”。希望这些题目能够帮助你更熟练地运用过去完成时来表达复杂的时态关系。如果还有任何疑问，欢迎继续探讨！