请帮解这选择题 关于比较的 she is ----- a fool than i thought.

请帮解这选择题 关于比较的 she is _____ a fool than i thought.
she is _____ a fool than i thought. she is quite smart.
A more of
B more than
C less of
D less than
答案是C 我不太明白这几个结构 尤其是D为什么不对 ,请帮解释一下 谢谢啊