Why do mammals require lungs? Provide 3 reasons.

All life respires, or breathes. Respiration in mammals is similar to respiration in other air-breathing animals. Respiration extracts oxygen from the air, which is then used by cells. Respiration also carries waste carbon dioxide away from the cells. Although respiration depends on other systems, like the circulatory system, to take oxygen and carbon dioxide to and from cells, the respiratory system has the primary responsibility of bringing oxygen in to a mammal's body and sending carbon dioxide into the atmosphere.

Mammalian respiration occurs in the animal’s respiratory system. A respiratory system is made up of muscles and airways that work to bring fresh air into lungs where oxygen is exchanged in blood for carbon dioxide. The airways are often lined with hairs or other structures that help to clean the air of dust and microbes before it enters the lungs.

Mammalian respiratory systems rely on a single large muscle at the base of the lungs. This muscle is called a diaphragm. The diaphragm pulls the lungs downward to increase their volume, causing air to rush into the lungs. As it presses upward, the lungs become smaller, and air is exhaled. Muscles in the rib cage work in consort with the diaphragm to expand and contract the lungs.

Most likely a is the answer - because  you generate   38 atp's but also consume an atp.   each atp gives approx. less than 4 kcal so probably a is the closest answer.