请教大全416--主谓一致

1.        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（D）

(E) parts of the plant which are the most nutritious, have shattered and fallen

在这个题中，20%是修饰the leaf还是修饰the leaf and small stem material？如果只修饰前者，则主语结构变成n1 and n2，谓语应该用复数；如果修饰两者，主语则变成百分数 of + n结构，谓语单复数由后面的n单复数决定。但此题中n是n1 and n2的形式啊，尽管两个n都是单数，n1 and n2的形式还是应该算复数吧？

不知道我有没有说清楚。。。有点糊涂了，望nn指点