单选题 By the time he arrives in Beijing, we ______ here for two days.
   A) will have stayed                    B) shall stay
   C) have been staying                  D) have stayed
【正确答案】 A
【答案解析】词组by the time意为“在……之前”，它引导的句子用现在时表示将来时间，故主句需用将来时。再由stay这个动作一直持续着，故用完成时。