Engines are to machines what hearts are to animals.我知道这是A is to B what C is to D.的结构,但请问在此句中what hearts are to animals在句中做什么成分?状语?还是其他什么?what 做什么成分呢?

Question

Engines are to machines what hearts are to animals.
我知道这是A is to B what C is to D.的结构,但请问在此句中what hearts are to animals在句中做什么成分?状语?还是其他什么?what 做什么成分呢?

Answer 1

从结构上看,what分别做Engines are的表语和hearts are 的表语,同时,what应该理解成something as,也就是,原句可以理解为：
Engines are something to machines as hearts are (something) to animals.
既然“颖姿11 - 秀才 二级”对此题的正确性提出疑问,现不得不增加说明：
外研社出版的《英汉多功能词典》P.1699(左侧)关于what做关系代词的用法③说的非常清楚.有疑问的人自己查阅吧.
2006年高考英语山东卷答案有错,是因为它的选项有错,并不意味着楼主的这句Engines are to machines what hearts are to animals.也错.