My watch is missing. I can't find (it) anywhere.

Her father has gone abroad. Have you heard about (it)?

b.泛指时间、日期、距离、天气、地点、温度、距离、环境等。

　 It was nearly midnight when she came back.

It is noisy here.

It is about twenty minutes' walk from here to the bus stop.

II. 引导词：

a. 作形式主语, 代替由不定式, 动名词或从句表示的真正主语。其基本句型为： It (形式主语) +adj. + to+ v.

It (形式主语) +adj. + that (subject +v. )

e.g. It is important to know your limitations.

It happened that the harvest was bad that year.

It is said that there has an earthquake in Japan.

It is no business of yours where I spend my summer.

It remains to be seen whether it will do us harm or good.

b. 作形式宾语, 代替由不定式、动名词或从句表示的真正宾语。其基本句型为:

主语＋谓语＋it (形式宾语)＋宾语补足语＋to do sth. (doing sth. 或that从句).

e.g. Do you think it difficult to work out this maths problem?

Having been there many times, he found it easy to find Mr. Wang's house.