(A) : Acceleration of centre of mass depends only on the external force not on the internal forces.
(R ) : Internal forces are the force exerted by the particles on one another according to Newton.s third law they constitutes action, reaction pair and cancel each other.

Options

A. Both (A) and (R ) are true and (R ) is the correct explanation of (A)
B. Both (A) and (R ) are true and (R ) is not the correct explanation of (A)
C. (A) is true but (R ) is false
D. Both (A) and (R ) are false

Answer

A