Answer:
C. endocrine control, because melatonin is secreted into the blood and regulates body processes
Step-by-step explanation:
As mentioned in the question, melatonin is secreted by endocrine gland which is a part of human glandular or endocrine system. Endocrine system is responsible for secreting chemical messengers into the circulatory system of the humans, from where they travel to different target sites like brain.
Melatonin is also a chemical messenger which is secreted by pineal gland and travels through the blood stream to the targeted brain parts. When it reached the brain it directs it about the sleep wake cycle by causing lowered body temperature and increased drowsiness which together work in regulating sleep/wake cycle.
The endocrine system of the brain, is responsible for the regulation of melatonin secretion levels along with the hypothalamus region which get stimulated by light.
Therefore, C is the best option.
Hope it helps!