Concept:Gas exchange in humans takes place at a specific site where oxygen enters the blood and carbon dioxide leaves it.Explanation:The lungs are the paired respiratory organs located in the chest cavity.Inside the lungs, tiny air sacs called alveoli provide a large surface area for gas exchange.Oxygen diffuses from the alveoli into the bloodstream, while carbon dioxide diffuses from the blood into the alveoli.Although the diaphragm, bronchi, and trachea help move air, they do not carry out the actual exchange of gases.Answer:C. Lungs