在英语语法中，过去完成时是一个非常重要的时态，它用来描述在过去某个时间点之前已经发生的动作或状态。为了帮助大家更好地理解和掌握这一时态，下面我们将通过一些练习题来巩固相关的知识点。

练习题

1. By the time I arrived at the station, the train _______.

A) has left

B) had left

C) was leaving

D) would leave

2. She _______ her homework before she went out to play.

A) finished

B) had finished

C) finishes

D) has finished

3. When he got home, his mother _______ dinner.

A) cooked

B) had cooked

C) was cooking

D) cooks

4. They _______ the film by the time we joined them.

A) have seen

B) had seen

C) saw

D) were seeing

5. The teacher told us that the students _______ all the exercises by 5 o'clock.

A) had completed

B) completed

C) were completing

D) have completed

答案解析

1. B) had left

解析：由“by the time”引导的时间状语从句表明，火车离开的动作发生在到达车站之前，因此需要用过去完成时。

2. B) had finished

解析：她出去玩是在完成作业之后，所以这里需要使用过去完成时来表示“过去的过去”。

3. B) had cooked

解析：当他到家的时候，母亲已经做好了晚饭，因此这里也用过去完成时。

4. B) had seen

解析：当我们加入他们的时候，他们已经看完了电影，所以应该用过去完成时。

5. A) had completed

解析：老师告诉我们学生们在五点钟之前已经完成了所有的练习，因此这里也需要用过去完成时。

通过这些练习题，我们可以看出，过去完成时主要用于表达两个过去动作中的前者，即“过去的过去”。希望这些题目能够帮助你更好地掌握这一语法点！