The velocity of the car (D) is described for us.
In order to have a velocity, you need a speed AND the direction of motion.
A . . . we don't even now whether this 10 kg object is moving
B . . . we know the distance the truck traveled, but not its speed OR velocity
C . . . we know the object's speed but not its velocity
D . . . speed and direction are both there, so we know the velocity
