The v-t  graph of a moving object is given in figure. The maximum acceleration is  

• A

  $1 \mathrm{cm}/{\sec }^2$

• B

  $2 \mathrm{cm}/{\sec }^2$

• C

  $12 \mathrm{cm}/{\sec }^2$

• D

  $6 \mathrm{cm}/{\sec }^2$