()is to do good all one's life and never do anything bad

问题描述:

()is to do good all one's life and never do anything bad
a.whichever is hard
b.no matter what is hard
c.what is hard
d.all what is hard
为什么答案是c?
别的为什么都不对?
请给与解释

what is hard是作为整个句子的主语