battlefields是复数，还是说only是做adv修饰eight？？
2.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.
(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
正确答案是D，C哪里错了呢
3.In the most common procedure for harvesting forage crops such as alfalfa, as much as 20 percent of the leaf and small-stem material, which is the most nutritious of all the parts of the plant, shattered and fell to the ground.
(A) which is the most nutritious of all the parts of the plant, shattered and fell
(B) the most nutritious of all parts of the plant, shatter and fall
(C) the parts of the plant which were most nutritious, will shatter and fall
(D) the most nutritious parts of the plant, shatters and falls
(E) parts of the plant which are the most nutritious, have shattered and fallen
D
这个题虽然选对了，但是还是有疑惑
不是说百分比的主语要看后面的名词么，这句话的主语应该是the leaf and small-stem material吧，但是为什么后面的动词是用的单数形式呢？
谢谢~