表示一种句型结构：It is + 形容词 + for(或of) 某人 to do 某事例如：It is difficult for him to come.要他来是有困难的；It''s kind of you to give me a present.这真好，你送我礼物；It is impossible to master English in a month or two.要在一两个月内精通英文是不可能的；It is important for us to learn English well.对我们来说,学好英文很重要；It is best to do it yourself. 最好是你自己动手。