In order to maintain homeostasis, the systems of the human body work together to keep a constant internal temperature. Which of the following best describes how the human body responds in a cold environment ? A. The digestive system produces more hormones to warm the body. B. The nervous system signals the muscles of the muscular system to contract and warm the body. C. The circulatory system delivers less carbon dioxide to the muscular system, resulting in stiffening of the muscles. D. The skeletal system produces more blood cells that circulate through the blood vessels, increasing the warmth of the body.