题目

―Was the doctor there when you arrived?   ―Yes, but he ______ out a moment later.   A. had gone      B. has gone C. went       D. is going 答案：C  从Yes可知，你到达时他在那里。又从but可知，他一会儿之后就出去了。故用过去式。  已知实数x，y满足则x－3y的最大值为_____________．