Circadian, rhythm is an endogenously driven cycle for biochemical, physiological and behavioral processes. In humans, the approximate duration of this'biological clock is

The 24 hours physiological cycle in all living beings is called the circadian rhythm.It is also known as the biological clock because it controls the various patterns in organisms such as hormone regulation, sleep and wake cycle, feeding habit, cell differentiation leading to growth of the organism, etc. Thus the correct answer is option D.