Which organ system has the principal function of protection, water retention, thermoregulation, vitamin D synthesis, cutaneous sensation and nonverbal communication?

THE SKIN

Explanation: The Skin is the largest organ of the body,it is located on the outside of the human body,it carries out several activities aimed at ensuring the well-being of a organisms.

The following are some of the activities of the Skin

Osmoregulation ( regulation of the internal environment through osmosis), protection (prevents certain substance from entering the body),Water retention ( holds enough water required for moisturizing the body), thermoregulation (manages the internal temperature of the body),Vitamin D synthesis, cutaneous sensation and nonverbal communication etc.

c is the answer because when something is left after something evaporates that shows the chemical change.