Which of the following statements about melatonin are correct?
I. Melatonin secretion increases in the evening in response to darkness and decreases at dawn in response to light.
II. Increasing melatonin levels stimulate the body, preparing it for waking up and staying awake during the day.
III. Melatonin is secreted by the hypothalamus.
IV. The night-time drop in core body temperature triggers an increase in melatonin secretion.
V. Melatonin levels vary during a 12-hour cycle known as a circadian rhythm.
II, IV and V
I, III and IV
I only
II and V
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