题目内容：

It is necessary ( ) others when they are in trouble.Do you think so?
A.for us to help B.of us helping C.of us to help D.for us helping

优质解答

it is +adi +of/for sb to do sth这个结构中,如果用of,中间的形容词是在描述sb.如果用for,中间的形容词是在描述动词不定式it is kind of you to help me.你帮助我,真是好心.kind 是修饰you的it is important for us ...