OE - B, and EYou can infer from the words "isolated," "hidden," and "untouched" that the blank must be in line with these adjectives. It wouldn't make sense for a beach to be hidden, untouched, and (A) morose, "gloomy and sullen," or (C) dilapidated, "in disrepair or run-down," so you can eliminate these choices. Choices (D) placid, "calm," and (F)
imperturbable, "incapable of being disturbed," are both tempting options because it is possible that an isolated beach would be both of these things. But the sentence doesn't rule out the possibility that the beaches could be less than placid, and just because a beach hasn't been touched yet doesn't mean it is immune from being disturbed in the future. You are left with choice (B) immaculate, "without stain or flaw," and (E) pristine, "untouched" or "uncorrupted," which are both synonyms of the adjectives used elsewhere in the sentence and therefore the correct answers.