Answer: HALF
Explanation:
CONTEXT CLUES AND I TOOK IT BEFORE
A. Response is the system's reaction to the stimulus.
It doesn't have to be irritability - not every stimulus is unpleasant. And also, it's not adaptability, because you cannot always adapt to a stimulus, for example, to pain.
The variables that i would predict to be regulated by the body using a homeostatic mechanism are; amount of pressure which moves fluids in the body; amount of heat in the body; amount of water in the body;
Homeostasis is best described as the maintenance of a stable internal environment in spite of a changing external environment.