例1 Great changes have taken place in China and it is not ________ it used to be. 中国已经发生了巨大的变化，再也不是以前的样子了。
解析 what。根据句意，分析句子结构可知，此处主句缺表语，故________ it used to be应是表语从句，故填what。
通过上面的例题可知，what引导名词性从句时充当成分，且一般是主语、宾语或表语（其功能相当于名词或代词）。
[意义归纳]
1. 表示“……的东西或事情”，相当于the thing that ...，all that ...，everything/anything that ...等。如：
Theyve done what they can to help her out of the present situation. What I have done share the same purpose—to help him out of trouble. 2. 表示“……的人或的樣子”，相当于the person/boy/girl/man that ...。例如： He is no longer what he was 20 years ago.
What he looks like makes him so special a man from others. 3. 表示“……的数量或数目”，相当于the amount/ number/weight/height/width/depth/length that ...。例如：
The number of the students in our school is ten times what it was before the economy was developed.
What I have earned by hard work can support me to do what I have been dreaming for.
4. 表示“……的时间”，相当于the time/day/hour/moment/year/decade/century/minute that ...。例如：
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。
I hate being cheated by others and wait there for what can last for a century. 我讨厌被别人欺骗，傻傻地站在那儿等别人。
5. 表示“……的地方”，相当于the place that ...。例如：
In 1492， Columbus reached what is now called America， hence， a new era came. 1492年哥伦布到达了现在所称的美洲大陆，从此，一个新的纪元开始了。 Now we are standing on what used to be a very famous place of interest； unfortunately， it was destroyed by the earthquake.
现在，我们站在一个风景名胜的遗迹上，不幸的是，这处名胜在地震中被毁掉了。 [用法解析]
纵观近年高考，对名词性从句的考查通常以在语法填空中设空填连接词或在短文改错中修改连接词为主。而这些连接词中，以对what的考查频率最高。掌握what的用法，准确辨析，对于名词性从句这一考点的掌握至关重要。
1. 引导名词性从句时，what相当于“先行词+关系代词”，所以其前不能有先行词。 例2 You can have everything what you like.
解析 去掉everything/what→that/去掉what。句意：你可以拿任何你喜欢的东西。此处everything是先行词，应用关系代词that引导定语从句。关系代词在定语从句中作like的宾语，故也可以去掉。再者也可以用what you like作have的宾语从句。
2. 有时what可用作限定词，修饰名词来引导名词性从句。
I do not know what steps I should take to deal with the recent situation. 3. What后的名词可以是复数名词或不可数名词，但通常不能是单数可数名词。 例3 I gave him what book I had.
解析 book→books。句意：我把我拥有的书都给了他。根据句意，book应用复数形式。 4. what后接不可数名词时，有时可用little修饰。 注意区别：
what+不可数名词=所有的都 what little+不可数名词=虽少但全部 例如：
I spent what time I had with her. 我所有的时间都是与她一起度过的。 I spent what little time I had with her.endprint 我仅有的一点时间都是与她一起度过的。
5. 除what外，在引导名词性从句时，还有whoever，whatever，whichever等也可引导名词性从句，其意分别为“所……的一切事或东西”“任何……的人”“……的任何人或物”等，并且充当成分。例如：
Whoever wants the book may have it. Ill do whatever I can to help him. [难点辨析]
从句意和结构上来看，where，when，which等引导词很好区分，唯有that和what的区分难度较大。
that在引导名词性从句时，从属连词that一般要注意：
1. 引导名词性从句时不能省略。当从属连词that引导主语从句、表语从句和同位语从句时，that不省略。
That he was willing to offer help made us very thrilled. （主语从句）
The fact is that you will never achieve personal success without a stable country and sustainable society. （表语从句）
The news that our team has won has inspired everyone of us to train harder to achieve further success and glory. （同位语从句）
注意 在非正式文体中，除下列两种情况外，that引导宾语从句时可以省略。 在“主语+谓语+it（形式宾语）+宾语补足语+that”句型中，从句（真正的宾语）中的that不能省略。如：
We will make it a rule that we both should sleep early and get up early.
由连词and连接的两个由that引导的宾语从句中，第一個宾语从句的that可以省略，第二个宾语从句前的that不能省略。如：
He told me （that） he would come and that he would come on time. 2. that引导名词性从句时不充当句子成分。
Sydney kept his promise that he would always do anything he could for Lucy to make sure of her happiness.
That you dont feel good about him has nothing to do with me. 3. that引导定语从句时没有任何词义，无法翻译，没有汉语意思。 That she is a rich woman is known to us.
The thought that he might fail in the exam worried him.
what在引导名词性从句时，相对that和what，一般有以下三个特点。 （1）what引导名词性从句时，在句中不省略，没有特殊情况。如： What I had for breakfast today was rice with egg. I want to give you what you have been looking for.
（2）what引导名词性从句时，有词义，一般翻译为“……的东西/事情/话/地方”等。如： This is what she wanted to show us. What she told me impressed me very much.
（3）what引导名词性从句时，必须作成分，一般是主语、宾语、表语，和名词、代词具有相同的功能。如：
What I have given to you is all free of charge.（此处what充当主语从句的宾语，谓语是given。）
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