A is to B what C is to D.

结构︰

A is to B what C is to D.

说明︰

此句型意为“A 之于 B 犹如 C 之于 D”。等于“A is to B as C is to D.”或“What C is to D (that) A is to B”或“As C is to D so is A to B”。这是为了让人明白 A 与 B 的关系，而利用人所熟知的 C 与 D 的关系来比喻的句法。what 是“A is to B”之 be <动词>的<补语>。

Exercise is to the body what thinking is to the brain.
运动和身体的关系，如同思考和头脑的关系。
What lungs are to the animal, leaves are to the plant.
就像肺是动物所不可缺的一样，叶子也是植物所不可或缺的。
As water is to the plant, so are books to me.
书和我的关系正如同水和植物的关系。