请教一道题，白勇语法全解2-39

白勇第二章39题

In terms of physics, the characteristic feature of the roller coaster is that the cars' potential energy, gained through their being lifted by a chain drive through the Earth's gravity to the top of the first drop, has been converted to kinetic energy by the time the ride ends.

1. cars' potential energy, gained through their being lifted by a chain drive
2. cars' potential energy, a gain achieved as they are lifted by a chain drive
3. potential energy from the cars' being lifted by a chain drive
4. potential energy of the cars, gained as a chain drive lifts them
5. potential energy gained by the cars, being achieved while a chain drive lifts them

答案D

BY对B选项的解释却是很让人费解。

其实很多题选的时候就凭语感和几个明显的错误，真分析下来，还真说不准错误原因……

对于这道题目个人觉得是

           1， 所有格的习惯表示， potential energy of the cars优于cars' potentials energy

           2， 用gained这个分词短语做energy的定语要好于用a gain这个同位语，因为前者更加简洁，表达也更流畅

           3， 一般能用主动的就不用被动，虽然这个规律争议很大，但在大多数题目中可以被验证