How does the behaviour of planets differ from stars, in terms of their motion in the sky, from night to night?
a. Planets move erratically and randomly across the sky from night to night.
b. All planets track around the North star in circles, whereas all stars do not.
c. The motion of planets is identical to the motion of stars.
d. Planets slowly drift across the sky relative to the background fixed stars, and occasionally move backwards or in retrograde loops.