C 正确
it's +形容词+of sb to do (此形容词是修饰sb的)
如 it's very kind of you to say that.
it's +形容词+for sb to do (此形容词是修饰to do sth的)
如it's necessary for you to finish it now.
to finish it now is necessary
不是you are necessary.
C 正确
it's +形容词+of sb to do (此形容词是修饰sb的)
如 it's very kind of you to say that.
it's +形容词+for sb to do (此形容词是修饰to do sth的)
如it's necessary for you to finish it now.
to finish it now is necessary
不是you are necessary.