非谓语动词的用法

It is foolish to act in this way.
It sounds reasonable to do it this way.
It appears likely for them to arrive.
2) 动词作谓语（常见的动词有：require, cost, amuse, delight, irritate, annoy
It took much time to do this.
It makes us excited to think about that.
It needed hard work to finish the job.
It does no good to say like that.
It didn't occur to me to ask him to help me.
3)名词作表语
It seems a pity to waste them.
It is a great pleasure to do this
It is a good idea to think this way.

动名词

 动名词表求比较抽象（一般）和经常性的意义，有时可同不定式互换 Collecting stamps is a good hobby.
Swimming is a best sport in summer.
There is no telling what will happen.
There is no denying the fact.
There is no need informing him of it.  动名词短语作主语时，常见的另一种形式是在句首用先行代词it作形式主语面将动名词短语移至谓语之后作真实主语。用于这种形式是一些特定形容词和名词 1)形容词作表语(常见的形容词有：enjoyable, good, hard, worthwhile)
It is nice talking to you.
It's foolish behaving like that.
It is useless doing that
2)名词作表语
It's waste of time doing this.  It's no good (use) doing that.
It's an awful job doing this.   It's fun doing this