在过去完成时的学习过程中，掌握其用法和结构是至关重要的一步。为了帮助大家更好地理解和运用过去完成时，以下是一些精选的练习题及详细答案解析。
练习题：
1. By the time I arrived at the station, the train ____________ (leave).
- A) has left
- B) had left
- C) was leaving
- D) would leave
2. She realized that she ____________ (forget) her keys at home.
- A) has forgotten
- B) had forgotten
- C) was forgetting
- D) would forget
3. When we got to the cinema, the movie ____________ (start).
- A) has started
- B) had started
- C) was starting
- D) would start
4. He said he ____________ (finish) his homework before dinner.
- A) has finished
- B) had finished
- C) was finishing
- D) would finish
5. By the end of last year, they ____________ (complete) the project.
- A) have completed
- B) had completed
- C) were completing
- D) will complete
答案与解析：
1. B) had left
解析：当“by the time”引导的时间状语从句中提到的动作发生在主句之前时，主句应使用过去完成时。
2. B) had forgotten
解析：这里强调的是在意识到之前已经忘记钥匙的动作，因此需要用过去完成时。
3. B) had started
解析：描述到达电影院时电影已经开始的状态，主句动作发生在过去，而开始的动作发生在更早之前。
4. B) had finished
解析：他所说的完成作业是在晚餐之前，这是一个过去的过去完成的动作。
5. B) had completed
解析：“by the end of last year”表示到去年年底为止，是一个过去的时间点，因此需要使用过去完成时。
通过这些练习题，大家可以更好地理解过去完成时的应用场景和结构。希望这些题目能够帮助大家巩固知识点！
