Concept:Air moves from the larger airways to the smaller air sacs in the lungs.Explanation:Air enters through the trachea.The trachea branches into the two bronchi.Each bronchus divides into smaller passages called bronchioles.Finally, bronchioles end in tiny air sacs called alveoli, where gas exchange occurs.Answer:C. trachea ⇢ bronchi ⇢ bronchioles ⇢ alveoli