for和of用法的区别

1.It's necessary ___for___us to master a language.
2.It's unwise ___of___them to refuse our help.
3.It is very important ___for__us to study some rules.
4.It is unpracticable ___for___us to finish such a difficult task
in such short time.
5.It's wrong __of / for___a person to think only of himself.（这一句for / of 都可以,看你站在什么立场上,出题人不太严谨）
窍门：
如果被认为是普遍现象,就用for,如：
1.It's necessary ___for___us / people to master a language.
2 It is very important ___for__us / learners to study some rules.
3 .It is unpracticable ___for___us / anyone to finish such a difficult task in two days.
如果被认为是某个人的个别现象,我们就用of,如：
1 It was wrong of me / John / us / the girl to be late again ans again.
2 It is very kind of him to give us so much help.(也就是说,he肯,但别人不一定肯)