求教 大全401

1.                         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.fficeffice" />

(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

答案D. 我不明白这里gained是充当什么成分?有人能帮我解释一下吗?

我选B,认为a gain 充当energy的同位语.看了其他的帖子说B用了被动不如主动好,但我还是不明白D中,gained是充当什么?

谢谢!