Life in the 21st century is much better than used to be.A. thatB. itC. what D. one

问题补充：

Life in the 21st century is much better than used to be.

A. that

B. it

C. what

D. one

答案：

A. that

(答案→)B. it

C. what

D. one

解析：考察it做形式主语。本题中it代替前文Life in the 21st century做下文形式主语，其它选项没有这个用法，故选B。