Question

homeostatic mechanisms
keep variables exactly at the set point
help to keep a relatively constant internal environment in the body
act to keep values out of the normal range
usually operate by positive feedback

Explanation:

Homeostatic mechanisms work to maintain a stable internal environment in the body. They don't keep variables exactly at set - point but within a normal range, and usually operate by negative feedback.

Answer:

help to keep a relatively constant internal environment in the body