Which of the following is not a good example of uniform circular motion?

a) a person riding on a ferris wheel that is turning at a constant rate
b) a person taking off on an airplane to fly around the world on a path defined by the equator
c) a race car driving at a constant speed around a circular track
d) a subatomic particle traveling at a constant speed in a circular accelerator

Aren't all these examples of centripetal acceleration? I can't rule any one of these choices out. =0