求教关于xxxpercent of的单复数

.       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

请问percent of +可数名词，谓语应该是单数还是复数呢？

谢谢

BY上的说法是百分数 of+名词，由名词的单复数决定谓语的单复数。由时态可排除ace

个人觉得这里as much as 表明了单数的含义。而且B中the most nutritious of all parts of the plant表意也不明确

情况不同用法不同。

50 percent of 200 students have completed the course.

1 percent of 50 students has completed the course.

同意愁予，as much as 确实表明要用单数，后面用 shatters and falls.20 percent of the stern material是不可数。