it引导从句与that them this区别

题目

it引导从句与that them this区别
The internet has made( )possible for people to communicate with each other whenever they like
A.THAT B.IT C.THEM D.THIS

答案

B
这里是固定搭配 it在这里做形式宾语.
that them this 引导从句时 从句里会有有主语,