Concept:The sentence requires the correct particle to form a phrasal verb meaning "to reduce the importance of something."Explanation:The phrasal verb is "play down."It means to make something seem less important or serious than it really is.For example: "He tried to play down his role in the success."Among the given options, only "down" combines with "play" to express this idea.Therefore, the correct word to complete the sentence is "down."Answer:D. down