Answer:
C) a longer circadian cycle
Step-by-step explanation:
Circadian cycle is a 24-hour physiological cycle which runs internally in the biological organisms in the brain and controls the sleepiness and alertness in individuals thus is also known as the sleep-wake cycle. The cycle runs in organisms of animals, plants and fungi.
The circadian cycle is controlled by the hypothalamus but the external factors like the intensity of light and dark also influence the circadian cycle.
In the given question, if the person has a disease which prevents eyes from perceiving light or the phase of darkness increases then the circadian cycle changes and become longer as the low light sends a signal to the brain to release melatonin which makes your body tired.
Therefore longer darkness means the increased circadian cycle and thus Option-C is the correct answer.