In a system of particles,internal forces can change (for the system)

Choose the correct statement$(s)$:
$(A)$ The position of the centre of mass of a system is dependent on the choice of coordinate system.
$(B)$ Newton's second law of motion is applicable to the centre of mass of the system.
$(C)$ Internal forces cannot change the state of the centre of mass.
$(D)$ Internal forces can change the state of the centre of mass.

Assertion $(A):$ If there is no external torque on a body about its centre of mass,then the velocity of the centre of mass remains constant.
Reason $(R):$ The linear momentum of an isolated system remains constant.

Internal forces can change

Internal forces acting within a system of particles can alter

Why do internal forces acting within a system not affect its motion?