change is to people what water is to fish.(请问,这句话里面有什么语法结构,what是怎么用的?)

问题描述:

change is to people what water is to fish.(请问,这句话里面有什么语法结构,what是怎么用的?)
意思倒是看懂了,但这是一个句子吗,该怎样理解?

what是,