Question

In my opinion, life in the twenty-first century is much easier than ________.

In my opinion, life in the twenty-first century is much easier than ________.

A. that used to be B. it is used to C. it was used to D. it used to be
选D，为什么不可以用what it used to be？
有什么区别，如何判断？

Answer 1

it 作为代词，代替前面的life充当主语

Answer 2

it 作为代词，代替前面的life充当主语