Which of the following statements is correct?

Options

A. If the centre of mass is at rest , then the net work done dy all the forces acting on the system is zero
B. If the velocity of the centre of mass remains zero, then the net external force acting on the system must zero
C. If the speed of centre of mass is changing , then there must be some work done by the internal forces on the system
D. If centre of mass of three - particle system is at rest and it is known that two of the particles are moving in different non - collinear lines , then third particle may be moving

Answer

B