Sentence Correction

IMO D.

This is a Subject-Verb agreement problem. First task is to find out what the subject of this sentence is.

Subject: 20 percent of the leaf and small-stem material

Is the Subject singular or plural ? The word 'material' like the word 'furniture' is singular. So 20% of the material should also be singular.

So the Verb should be Shatters and Falls.

P.S.'which is the most nutritious parts of the plant,' ( this is the modifier )

20% of the whole (singular/plural) will always need a singular verb

Hence D