句型“It is+adj.+(for sb)to do sth."和“It is+adj.+(of sb)to do sth."两个句型中， 在使用时要注意adj是说明sb的品质特点的还是说明to do sth的就可以了.说明sb的品质特点用of sb;说明to do sth用for sb.，
简单一句话说就是：说人的用of sb. 说事的用for sb。
1）for sb. 常用于表示事物的特征特点，表示客观形式的形容词，如easy, hard, difficult, interesting, importang,
impossible等：
It's very hard for him to study two languages. 对他来说学两门外语是很难的。
2）of sb的句型一般用表示人物的性格，品德，表示主观感情或态度的形容词，如good, kind, nice, clever, foolish, right。
It's very nice of you to help me. 你来帮助我，你真是太好了。
例:
It is difficult for him to finish the task within two hours.
(difficult 说明完成任务难)
It is kind of you to help me.(kind说明你善良)
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