The masses of two balls are in the ratio of $2$:$1$ and their respective velocities are in the ratio of $1$:$2$ but in the opposite direction before impact. If the coefficient of restitution is $1/2,$ the velocities of separation of the balls will be equal to

A$.$Original velocity in the same direction

B$.$Half the original velocity in the same direction

C$.$Half the original velocity in the opposite direction

D$.$Original velocity in the opposite direction