怎么区分of和for的用法

题目

怎么区分of和for的用法
有些句子of有些句子又要用for
请问怎么区分他们的用法啊
例如：
I worry _____ your health.
A.about B.of C.for

答案

of 是主观评价,如It's kind of you to help me.
for是客观评价,It's difficult for you to swim across the river.
而楼主所举例题选A worry about为固定词组