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 -- past tense is incorrect(B) the most nutritious of all parts of the plant,
shatter and fall -- should be singular(C) the parts of the plant which
were most nutritious, will shatter and fall
-- 'were' is incorrect(D) the most nutritious parts of the plant, shatters and falls
-- Correct(E) parts of the plant which are the most nutritious,
have shattered and fallen
-- It's shattered up until this point? Wrong.Comparing B and D, 'the most nutritious parts of the plant' is better than 'the most nutritious of all parts of the plant'.
Answer is D.