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.
A is to B what C is to D 的句型(我也是刚刚知道的)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...