Two bodies of masses M and 4M initially at rest, start moving towards each other due to their mutual attraction. The velocity of their centre of mass when the first body attains a velocity $\mathrm{v}_0$ is

• Correct answer
  A

  zero
• B

  $-v_0$
• C

  $2 \mathrm{v}_0$
• D

  $-4 v_0$

Hence, the correct answer is option: 'A'.