http://www.zybang.com/question/2fe89a222c9ee96c79dd545054733bfb.html
be +形容词为什么要再加of 有没有一些例句
英语
tafejh922014-11-02
优质解答
it is +adj of sb to sth 
此结构中,形容词多是【修饰sb】,表明【人所具有的品质、特点】.常用的形容词有nice,kind,fine,honest,true,good,friendly,enthusiastic,warm-hearted,/bad,cruel,cold-blooded等.例如：
It's kind of you to say so.
可以转换为：You are kind to say so.
It's nice of you to help me.=
It's polite of you to do so.
区别：It is +adj for sb to do sth 
这个结构中,形容词多是【修饰sth】,表示【不定式短语内容所体现出的特点】.常用形容词有：important,unimportant,difficult,hard,easy,necessary,unnecessary ,helpful,useful等.
例如：
It's important for us to learn a foreign language .
可以转换为To learn a foreign language is important for us.