It's very kind---you---so much money for us

选B绝对正确!
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.