A large number of trees are being cut down to make paper.

问题描述:

A large number of trees are being cut down to make paper.
里面的are being是什么意思,合在一起的?怎么用?说具体点,谢谢

正在被.现在进行时的被动用法,表示主语与宾语的关系,只是这里宾语省略,本来应该在cut down后面还有个by people 英语里面都省略了.