(1) “It is...for sb./sth. to do sth.”句型常用来说某人做某事是好是坏，是否必要，应不应当，对与不对等，其中for sb. to do sth.是实际主语，it为形式主语；而“It is...of sb. to do sth.”句型则表示因某人做了某事而对其本人的赞扬或非难。

• It is good for you to be here.
  你在这里是很好的。
• It is wrong for you to do that.
  你那样做是错误的。
• It is kind of you to take so much trouble for me.
  非常感谢你为我担了这么多麻烦。
• It was foolish of him to talk like that.
  他那样讲话真是愚蠢。
• It's wrong of you to laugh at others.
  你笑话别人是不对的。
• It is awfully good of you to come and meet us.
  非常感谢你前来迎接我们。
• It's unwise of them to turn down the proposal.
  他们拒绝这项建议是不明智的。
• It's only too easy for a young girl to go astray, especially if she is a stranger without friends.
  一个少女走入歧途是非常容易的，特别是如果她是一个初来乍到的陌生人而又没有朋友的话。

 (2) 在“It is...for sb. to do sth.”句型中(有时for接there to be形式)，常用以下三类形容词。

①表示重要性或紧急的形容词，如：important, unimportant, essential, vital, necessary, unnecessary, pointless。

• It's essential for the classrooms to have plenty of light.
  教室里光线充足是非常重要的。
• It's important for there to be a fire-escape.
  有一个太平梯是很重要的。
• It's vital for a person to have a correct view of life.
  一个人有正确的人生观是非常重要的。
• It's important for the accounts to be ready by Friday.
  重要的是要在周五前把这些账目准备好。

②表示频率的形容词，如：common, normal, unusual, rare。

• It is unusual for foxes to come so close to the town.
  狐狸跑到距城镇这么近的地方是不寻常的事。
• Do you think it's normal for a child to get so tired?
  你认为一个小孩这么疲劳正常吗？

③表示轻重、早晚、难易等的形容词(常有too, enough, not修饰)，如light, heavy, early, late, difficult, easy等。

• I think it's too late for us to catch the 7:50 train.
  我认为我们要赶7：50的火车太迟了。
• I think it's early enough for you to go to school now.
  我认为你现在去上学是够早的了。

 (3) 在“It is...of sb. to do sth.”句型中，常用对人的性格、行为、态度、品质等表示赞扬或非难的形容词，如：kind, unkind, silly, careless, naughty, nice, good, considerate, foolish, right, wrong, wise, unwise, polite, impolite, cruel, rude, impudent, stupid, absurd, ungrateful, unmanly, mad, clever, ill-natured, wicked等。