[求助]求解一道题

Anniesmiling

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 convened to kinetic energy by the time the ride ends.

A. cars' potential energy, gained through their being lifted by a chain drive

B. cars' potential energy, a gain achieved as they are lifted by a chain drive

C. potential energy from the cars' being lifted by a chain drive

D. potential energy of the cars, gained as a chain drive lifts them

E.  potential energy gained by the cars, being achieved while a chain drive lifts them

选D

请大虾明示点解? C错在哪里? 

focusspeed

car's 的所有格后面应该用名词