A:Would you mind my smoking here?
B: ______. Look at the sign. It says" No smoking."
A:You're welcome.
B:Certainly not.
C:You'd better not.
D:Never mind.
如图所示,小球从距离地面一定高度的O点沿x轴竖直落下,不计空气阻力,图象表示小球某种形式的能量E随下落高度x的变化情况。E可能表示小球的( )