【题目】—Hello! Is Mr. John in the office?
—Yes. But I'm sorry. He is busy ________ and can't speak to you.
A.at once
B.at present
C.at the end
D.at first

【答案】B
【解析】句意：他现在很忙，不能和你说话。at once”立刻“；at present”现在，目前“；at the end”在.....末端/终点“；at first”起初“。因此答案选B。