It is difficult when I think about what my friends are doing now.结构分析

题目

It is difficult when I think about what my friends are doing now.结构分析
It is difficult when I think about what my friends are doing now.
我知道这是个主语从句.
想请问" what my friend are doing now" 这部分是从句吗?
如果是,是什么从句?

答案

it是一个形式主语 真正主语是when I think about what my friends are doing now
所以还原的话是when I think about what my friends are doing now is difficult.
而about是一个介词 介词后what my friends are doing now 则为宾语从句