请教nn一道语法题...谢谢:)

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

Bthe most nutritious fo 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

为什么答案d里是shatters 和falls呢？

楼主发帖很积极，但要每次标题中注明题号和正确答案会节省大家时间并利人利己。。。

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谢谢！祝复习愉快！