what引导比较状语从句 A is to B,what C is to D或者 What A is to B,so is C to D As A is to B,that C is to D 翻译成,A和B的关系正如C和D的关系一样 不能换成as,这是一个固定用语,在英语里是一个表修辞的句式(类比) 汉语意思是:A之于B正如C之于D 例:Air is to human what water is to fish. 空气之于人类犹如水之于鱼.有些托福的语法书上讲有的,或你也可参考《修辞学》黄任著(上海外语教育出版社)