Final answer:
Hyenas are nocturnal animals that sleep for long periods during the day, as they are mainly active at night.
Step-by-step explanation:
Among the choices provided for what a hyena does for long periods of time, the answer is (a) Sleeps. Hyenas are indeed nocturnal creatures, meaning they are active during the night and rest during the day. While the mythical image of hyenas laughing manically is popular in culture, it's not an activity they engage in for extended periods. Hyenas do hunt for food, but this is not a continuous all-day activity. They are efficient hunters and scavengers but allocate significant time for resting.