A gun of mass M fires a bullet of mass m, with a Kinetic energy E. The total kinetic energy in the firing process is

• A

  $\left(\frac{M+m}{M}\right)E$

• B

  $\left(\frac{M+m}{m}\right)E$

• C

  $\left(\frac{M}{M+m}\right)E$

• D

  $\left(\frac{m}{M+m}\right)E$