基本结构

- I had finished my homework before supper.（晚饭前我就完成了作业）

- The letter had been sent before he left.（他离开前信已经寄出）

时间状语从句

- By the time we arrived, the meeting had already started.（我们到达时会议已经开始）

- Whenever she called, he had already finished his task.（她每次打电话时，他都已完成工作）

结果与影响

- The cake had melted in the microwave, so I had to start over.（蛋糕在微波炉里融化了，所以我不得不重做）

- I didn’t know the word, for I had never heard it before.（我不知道这个词，因为我从未听过）

间接引语

- He said he had never been to that country.（他说他从未去过那个国家）

- They reported that the project had been completed on time.（他们报告说项目已按时完成）

与过去简单时的对比

- I had already eaten breakfast when you called.（你打电话时我已吃过早餐）

- She had finished her degree before he started his business.（她毕业前他就开始创业）

其他用法

- The movie had ended when we got home.（我们到家时电影已结束）

- I had left the house for two hours when the phone rang.（电话响时我已离开家2小时）

这些例句覆盖了过去完成时的主要用法，包括时间状语从句、结果表达、间接引语等场景，帮助理解其核心功能是描述“过去的过去”事件。