2. A is to B what C is to D. 

钟老师认为这个句子不对，想听听钟老师解释不对在哪里？

钟老师认为应该加is。即：

A is to B is what C is to D. 

愿闻钟老师分析这个句子结构。

A is to B what C is to D 这个句式以前我也参与过解答。它是在比喻类修辞手法中，使用关系词what比较有名的一个固定句型：要分析其实很简单：

Reading is to the mind what food is to the body.

阅读之于心灵，犹如食物之于身体

食物和身体是什么关系？--不可或缺的关系。之所以提到这个食物和身体的关系，是为了让人明白阅读对于心灵同样不可或缺。所以，what后面的部分是为了让人理解前半句的主张而举的例子而已。所以，该句型隐含有“A和B之间是不可或缺的”关系：

所以，AB之间的关系是作者的观点，CD之间的关系是作者的举例，让读者更好地理解自己的观点。

注意两点：

1）what前后为物与物的比较，如果为数字（字母）与数字（字母）的比较，常用as替代what：

a:b = c:d  

a is to b as c is to d

2）如果what从句提到句首，后面的主句一般用that（不是is）连接，也可以省略that：

What sculpture is to a block of marble, education is to the soul.

教育之于心灵，犹如雕刻之于大理石。（省略that，但不要添加is）

What salt is to food, that wit and humor are to conversation and literature.

妙语与幽默之于会话与文学，恰似盐与食物一样。

了解了这些，相信你使用这个句型不会出错。附带说一句，说这个固定句型是错误的外教，建议查查对方的教育程度，其文凭是否来自文凭作坊，然后让对方滚蛋。:))

这是一个“特殊比较句式”（A is to B what C is to D），通常不作语法分析，会用既可。如果一定要分析的话，Air是主语，to us是状语，意为“对于我们来说”，后面的what为融合型关系代词（先行词+定语从句）引导名词性关系分句，即相当于一个名词词组作主句的表语。不过，它的作用却相当于一个比较状语从句，所以也可将其看作比较从句的特殊用法。what理解为(just) as“恰似；犹如；好比”，意为“A对于B来说，犹如C对于D一样”。又例如：

The house is to the man what the nest is to the bird.鸟儿的巢就如同人的房屋。

A CPU is to a computer (just) as a heart is to a human. 中央处理器对于电脑来说就如同人的心脏。

▲答疑网不止一次回答过此类问题，选择其中两个（供参考）：

http://ask.yygrammar.com/q-3112.html

http://ask.yygrammar.com/q-29371.html

3）特别感谢深圳钟老师的提醒, 我引用时疏忽了：What C is to D, that A is to B 不是正确的句子，这点我和深圳钟老师看法一致，有不同意见的老师或网友，请分享几个英文原著中的句子。正确的写法应该是：What C is to D, that is A to B. （What从句前置，做that的同位语）

凡哥英语老师好，我找几个例子，不知道句子正确不正确，您可以鉴定一下。

The Works of the Right Reverend William Warburton, D.D., Lord Bishop ...
https://books.google.ae/books?id=fFIJAAAAQAAJ
William Warburton, ‎William Warburton (Bp. of Gloucester), ‎Richard Hurd - 1811 - ‎Theology
For what light is to the eye, that knowledge is to the mind : On which account it is become a metaphor running through all languages, but hath a peculiar grace ...
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Henry Cowles : The Revelation of John (1871) Free Online Books ...
Henry Cowles : The Revelation of John (1871) Free Online Books @ PreteristArchive.com, The Internet's Only Balanced Look at Preterism and Preterist Eschatology

What light is to the eye, that knowledge is to the mind. Hence the teachers of truth are in symbol, light-bearers. 13. And in the midst of the seven candlesticks one ...

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A View of the History, Literature, and Religion of the Hindoos: ...

https://books.google.co.jp › books

William Ward - 1817 - ‎Hindu mythology

... from nimiik, salt, and haram, faithless. I suppose this allusion intimates, as an Eastern compliment, that what salt is to food, that a master is to his servant.

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GMAT - Comparison - Manhattan & Ron Flashcards | Quizlet

https://quizlet.com › gmat-comparison-manhattan-ron-flash-cards

What blood vessel is to a man's body, that railway is to transportation.（=Just as blood vessel is to a man's body, so Railway is to transportation.）

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What C is to D, that A is to B这个语序，在以下书上有出现：

《薄冰英语惯用法词典》

《现代英语语法大全》（赵俊英）

《当代高级英语语法》（徐广联）

http://ask.yygrammar.com/q-31940.html

A is to B as/what C is to D. 

主句：A is what C is(to B为主句状语，to D为从句状语）

在以上结构中：what从句是名词性从句，what既引导表语从句，同时在从句中做表语。（名词性表语)。to B和to D分别是主句和从句的状语。

http://ask.yygrammar.com/q-23737.html

A to B is what C to D”中，A.B均为本体，C.D均为喻体，“what”作为连词使用，意思是“恰如、好像、相当于”， what前后为物与物的比较，如果空格前后为数与数的比较，则要用as连接，

Four is to twelve as one is to three．4比12等于1比3。

Food is to the body what reading is to the knowledge．

食物对于身体正如读书对于知识。

Oxygen is to the human beings what water is to the fish．

氧气对于人类就像水对于鱼。

Reading is to the mind what food is to the body.

读书之于心灵，犹如食物之于身体。

Three is to four as six is to eight. 三对四之比等于六对八之比。

Air is to man as water is to fish. 空气之于人犹如水之于鱼。

Water is to fish, as air is to men. 水之于鱼，犹如空气之于人。

这样用的 as 也可以换成 what。如：

Manure is to crops what food is to man. 

肥料对于农作物，就如同食物对人一样。

Engines are to machines what hearts are to animals. 

发动机对机器之关系犹如心脏对动物之关系。

关于“A is to B as C is to D.”的句式，第2种解答

Leaves are to the plant what lungs are to the animal.

叶之于植物犹如肺之于动物。

Regulation is to a school what the law is to a nation.

校规之于学校，犹如法律之于国家。

这个句型与下列句型相似，试比较：

① A is to B what X is to Y 

② A is to B as X is to Y 

③ As X is to Y, so is A to B 

④ What X is to Y, that is A to B

在①、②句型中，what和as都用作连接词，其后是从句，主句在前。①句型可译为“A之于B等于X之于Y”，其中what X is to Y是名词从句，是动词is的补语，动词is可以省去。②句型可译为“A之于B犹如X之于Y”。③、④句型与①、②句型相反，主句在后，从句在前。③句型可译为“正如X之于Y，A对于B也表示同一关系”。在④句型中，作为补语的名词从句放在句首，用that作同格词，这个that可省去。注意③、④句型的后半句，主语和动词的位置转换了。

其他类似的例子：

Air is to us as water is to fish. 

空气对于我们，犹如水对于鱼一样重要。

Reading is to the mind what exercise is to the body.

读书对于思想，好比运动对于身体一样重要。

What the voyage of Columbus was to the world in the 15^th century, the journey of the satellite, Lunik Ⅲ, might well be to the twentieth. 

哥伦布的航行对于15世纪人们的意义，犹如3号月球卫星航行对于20世纪人们的意义一样。

As the house is to the man so is the nest to the bird and the cave to the animal

= The house is to the man what the nest is to the bird and cave to the animal.

= What the nest is to the bird and the cave to the animal so is the house to the man.

室之于人，犹巢之于鸟，穴之于兽。

Five is to seven what ten is to fourteen. 

五与七之比等于十与十四之比。