The answer is D. Velocity has a direction and a magnitude, so to have a constant velocity, none of them should be changing. A seems right at first, but when the cat climbs up a tree, it's changing directions. B says the cat slows down which means there's a change in velocity and acceleration is present. C says that the cat's running around in circles so it's constantly changing directions. D is the only right one because the magnitude of velocity (speed) is 0 and not changing neither is the direction.
