$A$ bullet of mass $m$ and speed $v$ hits a pendulum bob of mass $M$ at time $t_1$,and passes completely through the bob. The bullet emerges at time $t_2$ with a speed of $v/2$. The pendulum bob is suspended by a stiff rod of length $l$ and negligible mass. After the collision,the bob can barely swing through a complete vertical circle. At time $t_3$,the bob reaches the highest position. What quantities are conserved in this process?

• A
  Total kinetic energy of the bob and the bullet during the time interval $\Delta t = t_2 - t_1$.
• B
  Total momentum of the bob and the bullet during the time interval $\Delta t = t_2 - t_1$.
• C
  Total mechanical energy of the bob and the bullet during the time interval $t_3 - t_1$.
• D
  Momentum of the bob after $t_2$.