题干
If the pilot flies the plane in a clockwise circle, what does this mean?
A：It means "message not received”.
B：It means "message received and understood”.
C：It means "message received but not understood”.
D：It's not mentioned in the passage.
答案(点此获取答案解析）
C
的物体静止在光滑水平面上，从
时刻开始受到水平力的作用。力的大小
与时间
的关系如图所示，力的方向保持不变，则
时刻的瞬时功率为
