Circadian rhythms are controlled by the __________

A) pineal gland.
B) suprachiasmatic nucleus (SCN) .
C) thalamus.
D) hippocampus.

The suprachiasmatic nucleus (SCN) in the hypothalamus is known as the master clock of the body and controls circadian rhythms. The pineal gland also plays a role in circadian rhythms by secreting melatonin in response to signals from the SCN, but it is not the primary control center. The thalamus and hippocampus are important brain structures, but they are not directly involved in regulating circadian rhythms.