Running up a tree after running straight is a change in direction thus, although the speed is same 30mph, the velocity is different. Now, in choice B, the cat is slowing down after having escaped from the dog. This is also a change in velocity (because the speed decreases).When the cat is sitting still the whole time, its velocity is 0.0mph the entire time. That means the velocity doesn't change And when the cat is running around the house, the cat is changing direction (thus velocity is different).
(This is relevantly a circular motion, and acceleration is a non-zero constant, and thus veloicty of course isn't same).
