d. The muscles begin shivering on a cold, snowy day.
Homeostasis is the body's ability to maintain a stable internal environment, despite changes in the external environment. Shivering is an example of homeostasis because it is a response that helps the body maintain a stable internal temperature. When the body is exposed to cold temperatures, the muscles begin to shiver, which produces heat and helps the body maintain a normal body temperature. This helps to prevent the body from becoming too cold, which can be harmful to health.