Conservation Of Momentum

Two identical blocks $A$ and $B$ of mass $M$ each are placed on a smooth floor.

Now, a small block of mass $m$ is being released from the position shown in the diagram. Then the velocity of block $B$ is maximized when $\text{\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_}.$

A. $m$ is at the highest position on $B$
B. $m$ is at the lowest position and is moving to the left
C. $m$ is at $C$
D. $m$ is at the lowest position and is moving to the right