过去完成时态被动语态用于描述过去某个时间点之前已经完成的被动动作，构成为“had been + 过去分词”。掌握这种时态需要大量的练习，包括改写句子、填空和改写为肯定/否定/疑问形式等。
过去完成时态被动语态用于描述过去某个时间点之前已经完成的动作，同时强调该动作的被动性。该时态的构成为：had been + 过去分词。例如："The car had been repaired by the mechanic before it was sold."
与其他时态和语态一样，掌握过去完成时态被动语态需要大量的练习和应用。以下是一些练习的例子：
- 改写下列句子为过去完成时态被动语态：
- The teacher had checked the homework before class started.
- The company had already promoted the employee before he resigned.
- The government had ratified the treaty before the war broke out.
- 填空：
- The house __________ (paint) by the time we moved in.
- The cake __________ (eat) by the time I arrived at the party.
- The movie __________ (watch) by the time we got to the theater.
- 将下列句子改写为肯定/否定/疑问形式：
- The books had been returned to the library.
- Had the concert tickets been sold out?
- The project had not been completed on time.
