Someone who stays in a cave with no light alternates between sleepiness and wakefulness on about a 24 hour cycle. Why?

A) changes in temperature
B) a rhythm generated within the person's own brain
C) detection of tides and magnetic fields
D) learned habits

Circadian Rhythm

The biological clock within living organisms that follows a roughly 24-hour cycle, affecting various bodily functions such as sleep-wake patterns.

Brain Generated

Originated or produced by the brain, referring to processes, thoughts, or activities that have their source within the neural circuitry.

Light

Electromagnetic radiation within a certain portion of the electromagnetic spectrum, visible to the human eye.