$A$ light particle moving horizontally with a speed $v_1$ strikes a very heavy block moving in the same direction with a speed $v_2$. The collision is elastic. After the collision,the velocity of the particle is:

• A
  $2v_1 - v_2$ in the original direction
• B
  $v_1 - v_2$ in the original direction
• C
  $v_2 - 2v_1$ in the original direction
• D
  $2v_2 - v_1$ in the original direction