The correct answer is D). In sentence, the underlined word, which is "down", is a preposition.
In sentence D. ("Place the refuse down the garbage chute"), "down" is a preposition because it is followed by a noun ("the garbage chute"). On the other hand, "down" in sentence A. is not a preposition since it is not followed by a noun. Moreover, although "outside" can be a preposition, in sentences B. and C. "outside" is an adverb because it is not followed by a noun.