A bullet of mass A and velocity B is fired into a block of mass C and sticks to it. The final velocity of the system equals

• A

  $\left(\frac{\mathrm{A}}{\mathrm{A}+\mathrm{C}}\right)\mathrm{B}$

• B

  $\left(\frac{\mathrm{A}+\mathrm{C}}{\mathrm{A}}\right)\mathrm{B}$

• C

  $\left(\frac{\mathrm{A}+\mathrm{B}}{\mathrm{C}}\right)\mathrm{A}$

• D

  $\left(\frac{\mathrm{C}}{\mathrm{A}+\mathrm{B}}\right)\mathrm{A}$