在英语语法中，过去完成时是一种重要的时态，用来描述在过去某个时间点之前已经发生的动作或存在的状态。它通常用于叙述故事、描述过去的事件顺序以及表达因果关系等场景。为了帮助大家更好地掌握这一时态，下面提供了一些专项练习题，希望大家通过练习能够更加熟练地运用过去完成时。

练习题一：填空

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

2. She realized that she _________ (forget) to bring her keys when she was halfway home.

3. When we got to the restaurant, they _________ (finish) serving dinner for the day.

4. He told me he _________ (repair) his car before it broke down again.

5. They _________ (visit) several cities by the time they finished their trip.

练习题二：改写句子

将下列句子改为过去完成时：

1. She called him after she finished her work.

改为：She had called him after she finished her work.

2. The teacher explained the lesson after the students asked questions.

改为：The teacher had explained the lesson before the students asked questions.

3. We went to the park after it stopped raining.

改为：We had gone to the park before it stopped raining.

练习题三：选择正确答案

1. By the end of last year, John _________ (work) in the company for ten years.

A. worked B. has worked C. had worked D. was working

2. When I got there, the meeting _________ (already start).

A. starts B. started C. had already started D. has already started

3. By the time you called, I _________ (already finish) my homework.

A. finishes B. have finished C. had finished D. was finishing

通过以上练习题，相信大家对过去完成时有了更深的理解。记住，过去完成时的关键在于“过去的过去”，即在一个过去的时间点之前已经发生的事情。希望这些练习能帮助大家巩固和提高对过去完成时的掌握程度。继续努力学习，祝大家进步！