After a few minutes the rate of oxygen consumption decreased because

The answer is: C) The stress level of the mouse decreased, and it became relaxed.

The right answer is C. (This could be explained by the released hormones)
The mouse used to consume more oxygen because it was in a state of stress.It should be known that stress operates in two stages:*The acute reaction, where adrenaline circulates in us, and we feel the full effects.*The chronic reaction that is prolonged and can last (involving other chemicals such as corticosteroids), we do not perceive the effects, but can also disrupt our body.

Both adrenaline and corticoid rise oxygen consumption in the body. when the mouse is relaxed, the effects of these hormones disappeared, so the oxygen consumption decrease.