Final answer:
Sunspots occur in predictable cycles and are not permanent features on the Sun's surface, changing in number over time.
Step-by-step explanation:
The statement a. They occur in predictable cycles is true regarding sunspots. Sunspots are dark regions on the surface of the Sun caused by increased magnetic activity. They are not permanent features and vary in number over time. Sunspots occur in cycles called the sunspot cycle, which averages about 11 years in length. During a cycle, the number of visible sunspots fluctuates, with periods of high activity and low activity.