题目

 ---What did you discuss just now?       ---We discussed           .  A．when could we meet at Xinhua Bookstore  B．where we would have a wonderful outing  C．whether we will have a barbecue during May Day  D．who is suitable to be the host of the charity show 答案：B17．静止在水平桌面上的茶杯，桌子对茶杯的支持力和茶杯的重力是一对平衡力；茶杯对桌面的压力和桌面对茶杯的支持力是一对相互作用力．