In the most common procedures 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 plants,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 答案(D) 为什么D选项动词可以用单数呢 | 
