[求助]请教大全416，谢谢！

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

主语到底是什么，as much as 20 percent of the leaf and small-stem material应该怎么理解，是as much as 20 percent of （the leaf and small-stem material）还是（as much as 20 percent of the leaf ）and small-stem material，我觉得有歧义，而且，不管怎么理解都是A and B的结构啊，谓语为什么用单数？

谢谢！