Which hormone relates with temperature and sleep-wake cycle?

$I.$ Sleep-wake cycle,$II.$ Body temperature,$III.$ Pigmentation,$IV.$ Metabolism,$V.$ Defence capability. All of the above-mentioned activities are influenced/regulated by:

Which gland plays a very important role in the regulation of the $24$-hour (diurnal) rhythm of our body?

Melatonin is secreted by the . . . . . . .

Which of the following hormones helps in maintaining the normal rhythms of the sleep-wake cycle and body temperature?

The recently discovered hormones, melatonin and serotonin, are secreted at the ends of nerve fibres by the activity of: