过去进行时被动语态的句子结构为： was/were + being + 过去分词，表示过去某个时间正在被进行的被动动作。以下是典型例句及解析：

The cake was being baked when I arrived at the bakery.

我到达面包店时，蛋糕正在烘焙。

The road was being mended, so they couldn't drive on time.

因为道路正在修理，他们未能准时到达。

This time last year, we were planting trees here.

去年这个时候，我们正在此处种树。

The house was being painted when we went there.

我们到访时，房子正在粉刷。

The movie was being screened at the cinema.

电影正在影院上映。

注意事项：

被动语态中，主语为动作的接受者，如"the cake"（蛋糕）、"the road"（道路）等；

动作需用过去分词形式，如"baked"、"mended"等；

时间状语需明确指向过去某一时刻，如"when I arrived"、"this time last year"等。