in my opinion life in the 21st 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
为什么不选A,that不也可指代么?我学比较级的时候用来代指天气等不可数名次都用that啊 怎么这个不是呢》?