Look! Tom is too sleepy to work. He _____ up watching TV. [ ]

A. mustn't have stayed

B. shouldn't have stayed

C. mustn't stay

D. ought not to say.

关于重心，下列说法中正确的是（）

A.重心就是物体内最重的一点

B.形状规则的物体，重心在其几何中心上

C.物体所受重力只作用于重心上

D.物体的重心可能不在物体上