what当 what 用作连接代词，引导名词性从句时，可引导主语从句、表语从句和宾语从句；它本身在从句中充当主语、宾语或表语。1.what 表示“所的（事） ”的意思，相当于“the thing(s) that；all that；everything that ；等。例如：1)Leave it with me and Ill see what I can do.(what 引导宾语从句并作 do 的宾语)2)What you have done might do harm to other people.(what 引导主语从句并在从句中作宾语)2.What 表示“所的(人)”意思，相当于“the person that”等。例如：1)He is not what he used to be.他已不是从前的他了。(what 引导表语从句并在从句中作表语)2)She is no longer what she was five years ago.(what 引导表语从句并在从句中作表语)一.引导主语从句1) What we need is more time.2) What really matters is that she wore a pair of white shoes.3)What he said at the meeting astonished everybody present.4)What is most important in life isnt money.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. 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)三.引导表语从句1) Whether ways will be found to stop pollution or not is just what worries the public.2) That is what I want to tell you.3) .3)The little girl is no longer what she used to be.四.引导同位语从句1) They have no idea at all what he is working on.2) You have no idea what I suffered.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.补充：关系型 what 引导名词性从句的五种用法一、用法归纳1. 表示“的东西或事情”：Theyve done what they can to help her. 他们已经尽力帮助了她。What Mary is is the secretary. 玛丽的职务是秘书。2. 表示“的人或的样子”：He is no longer what he was. 他已经不是以前的那个样子。He is what is generally called a traitor. 他就是人们通常所说的叛徒。Who is it that has made Fred what he is now? 是谁把弗雷德培养成现在这个样子的？3. 表示“的数量或数目”：Our income is now double what it was ten years ago. 我们现在的收入是 10 年前的两倍。The number of the students in our school is ten times what it was before liberation. 4. 表示“的时间”：After what seemed like hours he came out with a bitter smile. 似乎过了几个小时他才苦笑着出来。The young girl was too frightened to speak, standing there for what seemed like hours. 小女孩吓得不敢说话，在那儿站了几个小时。5. 表示“的地方”：This is what they call Salt Lake City. 这就是他们称为盐湖城的地方。In 1492, Columbus reached what is now called America. 1492 年哥伦布到达了现在所称的美洲大陆。二、that 当 that 用作连接词，引导名词性从句时，可引导主语从句、表语从句、宾语从句和同位语从句，that在从句中既不充当任何成分，也无实际意义，仅起着连接句子的作用。一般不可省略（宾语从句除外） 。若从句置于句子后面，代词 it 作形式主语。例如：1)It worried her a bit that her hair was turning grey. (that 引导主语从句)2)It is a fact that The Diaoyu Islands are sacred Chinese territory.(that 引导主语从句)3)Can you believe (that)in such a rich country there should be so many poor people?(that 引导宾语从句)4)Tom felt that he knew everybodys business better than they knew it themselves.5)We heard the news that our team had won. (that 引导同位语从句)6)Another problem is that good soil is gradually lost. (that 引导表语从句)7)But the truth is that everyone should take care of disabled people, not just the government.