不是说have a difficult time to do sth

问题描述:

不是说have a difficult time to do sth
the old man had a difficult time____
a,to make a living
b.make a living
c.making a living
d.making a life
原因
我选了A
顺便问一下:D为啥不可以呢?

都是固定搭配.have a difficult time doing sth 和 make a living ,应该选C