GMAT Sentence Correction (SC) | Re: The U.S. Forest Service, then five years old, decided to put

This is definitely a question of adverb vs. adjective. The 3:2 split is 'quicker' vs 'more quickly'. Notice how we are talking about the verb form 'be extinguished'. Thus we must use the adverb form 'more quickly.' This narrows it down to (D) and (E). We are talking about an event in the past ('within three decades...'), so we do not want the present perfect 'has formulated.' That leaves us with (D).