The correct option is A melatonin
The pineal gland is an endocrine gland and is located on the dorsal side of the forebrain. It secretes a hormone called melatonin, which regulates the diurnal rhythm of our bodies.
Thyroxine is released by the thyroid gland. It regulates the metabolism in our bodies.
Somatostatin and gonadotropin releasing hormone (GnRH) are both secreted by the hypothalamus. Somatostatin inhibits the release of growth hormone from the pituitary. Gonadotropin releasing hormone stimulates the pituitary gland’s synthesis and release of gonadotropins.