___________is hard is to do good all one's life and never do anything bad A he B it C that D what

问题描述:

___________is hard is to do good all one's life and never do anything bad A he B it C that D what
为什么不选B 而选D?

选D
A,C一看就是错的.
选B的话应该是It is hard to do good……多了个is
D是对的.what is hard 是主语