[求助] XDF蓝皮书 动词时态问题

XDF蓝皮书动词时态专题第7题

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 nutrinious parts of the plant, shatters and falls

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

答案是D

划线部分修饰的到底是什么？这题除了考动词的时态外，还有什么考点？整句话该怎么理解呢？还请NN们多多指教，谢谢！

as much as 20 percent of the leaf and small-stem material, the most nutritious of all the parts of the plant,
            shatters and falls to the ground.

红色是同位语，黄色是谓语。除了考时态，还有主谓一致