Answer:
d) variability
Step-by-step explanation:
Variability is the quality of a service that does not follow a fixed, or predictable pattern, following instead a changing (or variable), or unpredictable pattern.
Seasonality is a type of variability that occurs when a business is subject to very rigid time constraints: in some periods of time it booms, and in other periods, it busts.
Alex's business is seasonal because it only becomes profitable during the summer months, while the other three seasons represent a net loss for him.