过去完成时被动语态的句子结构是 had been + 过去分词。以下是一些例句：
The work had been finished before I arrived.
The cake had been eaten by someone.
The room had been cleaned.
The project had been completed before the deadline.
The book had been read by many people before it was returned to the library.
The task had been finished before 12:00 yesterday.
The task hadn't been finished before 12:00 yesterday.
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，强调了在过去某个时间点之前已经完成的被动动作。