一般说来，不定式的被动式表示将要发生的被动动作，现在分词的被动式表示正在发生的被动动作，而过去分词则表示已经完成的被动动作。例如：
I have a problem to be discussed at the meeting. ( 将来)
The building being built on the river is the Science Museum. （正在进行）
The building having been built is our classroom building.
The building completed three years ago is now in bad conditions. （过去）
I still remember being taken to the Famen Temple and what I saw there.
