—Hi, Bob! What's going on over there?
—Oh, Tom and Dick are playing chess, with a crowd of students watching them.
A:happening
B:appearing
C:working
北京和广州两地自转角速度和线速度比较,正确的是( )
一个同学用100N的水平方向的力将一只足球沿水平方向踢了出去,足球在地面上滚动30m后停下.在球滚动过程中,脚对球做的功是 ____