as what 数与数

选B: Twelve is to three as four is to one. 如果要用what的话, 应该是：Twelve to three is what four is to one, 或者 What twelve is to three is what four is to one.

选A。这道题就象是Water is to fish what air is to human.不管是物与物的比较还是数与数的比较都用what.

这不是数与数的比较，而是短语与短语的比较。
所以用what

进一步说明一下，这个句型有如下用法：
A is to B what C is to D
A之于B犹如C之于D

what A is to B that is C to D
A之于B犹如C之于D

我是英语专业的，老师讲过这道题，选A和B都可以，但是B更合适。A is to B what C is to D 是这个句型，但是就像你说的，数与数比较就是用as，英语有的时候就是要靠记的，好好学吧。