单选题 No one has turned on the air conditioner______.

A、 (A) yet
B、 (B) never
C、 (C) already
D、 (D) soon

【正确答案】 A

【答案解析】Adverbs of definite frequency may appear at the end of a sentence. Choice (B) is an indefinite frequency adverb. Choice (C) is used with a completed action. Choice (D) indicates a future time.