Where, when, why等连接副词也可以引导名词性从句，使用的关键是：这个词必须符合句子的逻辑要求。例如 ：

- I drove to Zhuhai for the air show last week.

- Is that ____ you had a few days off?

A. why B. when C. that D. where (答案为A）

　　6、同位语从句引导词where, when的用法特点。

　　说明先行词内容的同位语从句的引导词where, when与被说明的名词在概念上不一致。但引导定语从句的引导词却必须保持一致。是比较：

　　Then arose the question ____ we were to get so much money. (答案为A）

　　This the house ____ the great man Mao Zedong was born 110 years ago.

　　A. where B. that C. about which D. in which (答案为A/D）

It的用法

1人称用法

人称用法是指it可以用来代替一个名词、一个短语、一个从句或一个句子，以避免它们在句中的重复。这时它可以指提到过的，也可以指未提到过的，在句中作主语或宾语。

（1）指非生物、动植物和不明性别的婴儿。That is a new magazine. I bought it this morning.

（2）指成员众多的集体

The acrobats performed for a large audience last night. It was very excited by the show.

（3）指某一动作或事情 I like dancing,but she doesn't like it.

2指示用法

　　指示用法是指it用在句型"It is/was+表语"中，指明某人或某物的身份。这时它可以代替this或that，作用同this或that，指提到过的或未提到过的。

What's that? It's a computer.

3先行用法

（1）指代不定式。How long does it take to travel from Beijing to Shanghai.

（2）指代动词-ing形式。以 It's no use, It's no good等开头的句子常以-ing分词作真正主语。

It's no good crying over spilt milk. It's no use trying to persuade him.

（3）指代名词性从句。 It is pity that you didn't see such a good film.

4无人称用法

（1）用于表示自然现象、时间、距离、环境等。 Is it cold in this room? No, it isn't.