A:a、b受力个数一定相等
B:b受到摩擦力可小于 a受到的摩擦力
C:a、b 所受摩擦力方向一定沿墙面向上
D:F1、F2大小一定相等
— Tom just told me a new way he had thought of new words.
— It's great. What do you think of it?
家用日光灯标有“220V 40W”的字样,该灯的额定功率为____ 瓦;家中电灯与电风扇之间是____ 连接的;测量家庭消耗电能的仪表叫____ 。