过去完成时被动语态用于描述在过去某个时间点或某个动作之前已经完成的被动动作。其结构是“had been + 过去分词”。以下是一些例句：

The work had been finished before I arrived.

我到之前，工作已经完成了。

The cake had been eaten by someone.

蛋糕已经被人吃了。

The project had been completed before the deadline.

在截止日期之前，这个项目已经完成了。

The book had been read by many people before it was returned to the library.

这本书在归还给图书馆之前已经被很多人阅读了。

The task had been finished before 12:00 yesterday.

昨天12点之前，任务已经完成了。

The classroom hadn't been cleaned before the teacher came.

老师来之前，教室还没有被打扫。

这些例句展示了过去完成时被动语态在不同情境下的应用，通常与时间状语如“before”连用，强调动作发生在过去的过去。