In the sentence "<em>It took </em><em>less</em><em> time to drive from one city to the other than they had anticipated</em>", the answer that correctly describes the bolded word is D:
<u>The word </u><u>less</u><u> is an adverb describing to what extent.</u>
In this sentence, the word less functions as an adverb; this means that it modifies or qualifies an adjective, a verb (in this case), or other adverb or a word group, expressing a relation of place, time, circumstance, manner, cause, degree, etc.