Final answer:
Option (A), The skin is the main body part involved in maintaining the body's heat balance, regulating temperature through mechanisms like vasodilation and sweating, supported by other features of the integumentary system.
Step-by-step explanation:
The main part of the body involved in maintaining the body's heat balance is skin. The skin is a critical component of the integumentary system, which also includes hair and nails; these elements work in conjunction to help the body maintain homeostasis, including the regulation of body temperature.
Mammals, including humans, use hair to trap heat, creating an insulating layer close to the skin. However, it's the skin that primarily regulates body temperature through mechanisms like vasodilation and vasoconstriction, which allow for heat dissipation or conservation by adjusting blood flow.
When the body needs to cool down, blood vessels in the skin dilate and sweat glands activate, increasing heat loss through evaporation.
In addition to the skin's role in temperature regulation, other features like nose hairs help filter particles from the air, while eyelashes and eyebrows offer additional protection for the eyes. Collectively, the skin and its appendages are integral to maintaining the body's heat balance.