Answer: (Option D) Insulin is most directly related to homeostasis.
Explanation: Homeostasis is the ability to maintain balance of body against a change in the environment. Insulin is a harmone which controls the glucose level in the blood. If the glucose level is high in the blood, the insulin gives message to the liver to absorb glucose from the blood and when glucose level is low, the liver released glucose into the blood. So insulin helps in the homeostasis of the body.