—Great! Everyone had fun.
A:How was the school trip yesterday
B:How often do you exercise
C:Did you ride a horse
D:Can you do the dishes
小明和小芳一起跳绳,小明跳了60下,小芳跳了48下,小芳再跳多少下就和小明一样多?
如图所示,四个棋子叠在一起静止在水平桌面上,一名同学用力迅速击打最下面的那个棋子,由于力可以改变物体的____,这个棋子飞了出去,上面的棋子由于____而保持静止状态,在____力的作用下落在桌子上.