Air to us is __water to fish.

Air to us is __water to fish.
A,what B,that C,which, D,of which.

老师说是根据结构,得出答案为A。
但是根绝结构,应该是。
A is to B what C is to D...
那么 Ais 是A,那本来是be动词的位置,不对。而且,从句中be动词也被省略了。// 所以，个人认为答案A有疑义//

希望有一个正确明了的解释//
注意：！！！！

Air to us is __water to fish
如果是按照句型的话，应该是：
air is to us what water is to fish.
而答案给出的是。
Air to us is what water to fish
// 不符合句型的// 希望能有专业点的回答。

Air to us is __water to fish. __ discovered america is well known to us all. __ is known to us all, the earth goes around the sun. The girl is __ to __ herself. water is important to us怎么写？ Friendship is spring bringing comforts to us I hope __(them to,they can )join us Let us go to the park,__ __? Let's go hiking,__ __?都变反意疑问句，有何区别 Mother is going to cook us ( ) to eat this Sunday. As is kown to all , biology is __