_____ is my responsibility to look after you

题目

_____ is my responsibility to look after you
a:it b:this c:that d:there
但b为什么不行?句意好像也行啊!这是我照顾你的责任.

答案

这里的it做形式主语,真正的主语是to look after you.This就不可以做形式主语了