Answer: C. happens daily
Circadian rhythms are processes that occur in a 24-hour cycle. A good example of a circadian rhythm is the appearance of fireflies at dusk because it happens daily, at a specific time. The time frame between the appearances of fireflies in two days is roughly 24-hours. Another good example of a circadian rhythm is the sleep-wake cycle in man. There is a designated time every day to sleep and this goes on consistently. Also, the opening and closing of petals of flowers is a form of the circadian rhythm.