dangerous等。

It is illegal (for a teenager) to drive a car without a license.

青少年没有驾照开车是违法的。

(2)It be＋adj.＋of sb.to do sth.

此处的形容词通常为描述人的形容词：kind，unkind，nice，rude，cruel，considerate，thoughtful，thoughtless，careful，careless，silly，foolish，stupid，clever，wise，crazy等。

It's kind of you to help me with the problem.

帮我解决问题，你真是太好了。

2．it作形式主语替代主语从句

(1)It is＋adj.＋从句

It is clear (obvious/true/possible/certain/...) that...

该句型中it 是形式主语，真正的主语是that引导的主语从句，常译为"清楚(显然，真的......)"。例如：

It is very clear that he's round and tall like a tree.

很明显他又胖又高像一棵树。

(2)It is＋v.­ed＋that...＝Sb./Sth.is＋v.­ed＋to do

It is said (reported/learned/believed/thought/known/told/hoped/...) that...

该句型中的it 仍是形式主语，真正的主语是that引导的主语从句；该结构常译为"据说(据报道，据悉......)"。

It is said that he has come to Beijing.

据说他已经来北京了。

It is reported that another earth satellite has been put into orbit.

据报道另一个地球卫星已发射进轨道。

(3)It is＋n.＋that...

It is a pity (a shame/an honor/a good thing/a fact/a surprise/...) that...

该句型中，如果表示出乎意料等感情，that后的从句一般用虚拟语气，即谓语动词用"should＋动词原形"，should可省去，常译为"竟然"。没有这种意义时，则不用虚拟语气。例如：

It is a pity that such a thing (should) happen in your class.

这种事竟然发生在你们班上，真是遗憾！

It is a pity that he is ill.他生病了，真遗憾！

四、it作形式宾语

当复合宾语中的宾语是不定式、动名词或宾语从句时，往往把宾语放在它的补足语后面，而用it 作形式宾语，放在宾语补足语之前。常用的动词有think，believe，make，find，consider，feel等。

I think it no use arguing with him.