What produces hand-cooling and hand-warming?

The correct choice highlights the physiological mechanisms involved in the regulation of blood flow to the hands, impacting their temperature. Hand-cooling is primarily associated with vasoconstriction, where blood vessels constrict, decreasing blood flow to the periphery and thereby reducing heat in the area. This is typically mediated by vasoconstricting fibers, which are part of the autonomic nervous system.

Conversely, hand-warming corresponds with vasodilation, where blood vessels relax and allow more blood to flow to the hands. This process is often influenced by vasodilating hormones, which contribute to increased circulation and warmth in the area.

Both vasoconstriction and vasodilation are critical regulatory mechanisms in maintaining body temperature and responding to environmental changes, thus explaining how these processes produce the sensations of hand-cooling and hand-warming. This answer embodies the intricate interplay between neural control and vascular responses that are fundamental to biofeedback and thermal regulation.