现已为婴儿特制成了一种新型的尿布——“尿不湿”。这种尿布表面涂有一种既能吸水又能保留水的物质。依你的推测，这种特殊物质的结构可能是
答案：C
—I didn’t see you when I went to your office yesterday afternoon. Where were you?
—I ____ a meeting in the meeting room.
A．have
B．will have
C．am having
D．was having
产品差异化导致产品替代性下降与以下哪些因素有关（）
A．差别定价
B．市场壁龛
C．定价权利
D．固定的客户群
