高三课本第十三单元有这样两句话：1)However，what happened later proved me wrong. 2)Franklin Blake，meanwhile，received a letter from Rosanna saying that she knew what he had done on the night the Moonstone disappeared.这两句话都运用了what引导名词性从句，如果我们平时常读英语文章或常做英语试题，就不难发现what的使用无处不在。下面就归纳总结what引导名词性从句的用法，希望对同学们有所帮助。

一.引导主语从句

1)What we need is more time.(what做need的宾语)

我们所需要的是更多的时间.

2)What really matters is that she wore a pair of white shoes.(what做matters的主语)

真正麻烦的是她穿了一双白鞋.

二.引导宾语从句

1)People were perhaps more honest a long time ago when life was very different from what it is today.(what做从句中is的表语)

很久以前当生活与现在的生活完全不同时，人们或许更诚实.

2)People have heard what the President has said;they are waiting to see what he will do.(what分别做动词heard和see的宾语)

人们已经听到了总统所说的；他们正等着看总统会做什么.

三.引导表语从句

1)Whether ways will be found to stop pollution or not is just what worries the public.(what做从句中的主语)

是否能找到阻止污染的方法就是所令民众担心的事儿.

2)That is what I want to tell you.(what做从句中的宾语)

那就是我想告诉你的事儿.

3)The little girl is no longer what she used to be.(what做从句中的表语)

这个小女孩不再是过去的样子了.

四.引导同位语从句

1)They have no idea at all what he is working on.(what做从句的宾语)

他们一点儿都不知道他正在做什么.

2)You have no idea what I suffered.(what做从句的宾语)

你不知道我所遭受的痛苦.

通过以上例句及解释我们可以得出：what常用来引导名词性从句，即主语从句，宾语从句，表语从句和同位语从句.what在引导名词性从句时有两个重要的特点：一是它在相应的名词性从句中一定有含义，常表示“什么”，“所…的”，“…的样子”等.二是它在相应的名词性从句中一定做成分，而且常做主语，宾语或表语.

练习：

1.It is not yet pretty welu nderstood_____made the rainforest disappear year by year.

A.that  B.when  C.what  D.how

2.The word media¹ basicaly refers to_______we commonly call newspapers，magazines，radios and televisions.

A.which  B.what  C.why  D.how

3.It's well understood_____controls the flow of carbon² dioxide³ in and out of theatmosphere today.

A.that  B.what  C.how  D.whether

4.The small mountain village____we spent our holiday last month lies in_____is now part of Hubei.

A.which;where  B.where;what  C.that;which  D.when;which

5.The reason why he was late was_____he had taken a wrong bus.

A.because  B.whether  C.what  D.that

6.Why is Li Ming so late？I don't know______.

A.can what the reason be B.what the reason can be C.the reason what can be D.what can the reason be

答案：C B B B D B