Let’s examine the sentence: “Both boxers trained very ___ for several weeks before the fight.” The blank requires a word to describe the quality or manner in which the boxers ‘trained.’ The blank requires an adverb of manner to add meaning to the verb ‘trained.’ Adverbs of manner are used to tell us the way or how something is done. This rules out Options A and C which are Adverbs of quantity. Option B contains the adverb “hardly” that tells you “almost never” about a verb. Option B cannot be used as it does not fit into the meaning of the sentence. Hence, Option D is the correct answer.