水的碱度，根据测定时所使用的指示剂不同或滴定终点的不同，可分为（）和（）两大类。
参考答案：酚酞碱度；甲基橙碱度
木块受水平力F作用在水平面上由静止开始运动，前进S米后撤去F，木块又沿原方向前进3S米停止，则摩擦力的大小为
A．F
B．F/3
C．F/2
D．F/4
-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 shall we have a barbecue during May Day
D．who is suitable to be the host of the charity show
