Answer: A). Alveoli
Explanation: Alveoli are important part of the respiratory system. They are tiny air sacs located at the end of the bronchioles in the lungs which functions in the exchange of oxygen and carbon dioxide. Alveoli is the plural of alveolus, and they are sites for the exchange of oxygen and carbon dioxide in the lungs. Deoxygenated blood is transported from the heart to the alveoli in the lungs through the pulmonary artery where carbon dioxide is unloaded from the red blood cells and oxygenated is loaded. The blood leaving the lungs becomes oxygenated and are transported to other parts of the body. Alveoli functions in getting oxygen into the blood stream and removing carbon dioxide from the blood stream.
