过去完成时是英语中表示在过去某个时间之前发生的动作的时态。例如，“我在父母回家之前已经完成了作业。”、“我们到达时，他们已经离开了。”等。掌握过去完成时的用法可以帮助我们更好地表达过去发生的事情。
- I had finished my homework before my parents came home. (我在父母回家之前已经完成了作业。)
- They had already left by the time we arrived. (我们到达时，他们已经离开了。)
- She had been studying English for two years before she moved to the United States. (她在搬到美国之前已经学了两年英语。)
- By the time I woke up, my friends had already gone to the park. (当我醒来时，我的朋友们已经去了公园。)
- Had you finished your work before the deadline? (你在截止日期之前完成了你的工作吗？)
- The train had left the station before we got there. (我们到达之前，火车已经离开了车站。)
- He had never seen snow before he moved to Canada. (他在搬到加拿大之前从未见过雪。)
- She had cooked dinner by the time her husband came home. (她的丈夫回家时，她已经做好了晚餐。)
- They had been married for ten years before they had their first child. (他们在生第一个孩子之前已经结婚十年了。)
- Had they finished the project before the presentation? (他们在演示之前完成了这个项目吗？)
