In a section of lung tissue consisting dominantly of alveoli, a tubule about 2mm in diameter is observed that contains smooth muscle and cailage in its wall. The tubule is which one of the following?: (A) Alveolar duct, (B) Alveolar sac, (C) Bronchiole, (D) Bronchus
Answer is D. Any tubule with cailage in its wall and contained in the parenchyma of the lung is a bronchus. Alveolar ducts, alveolar sacs, and bronchioles do not contain cailage. The trachea lies outside of the lung.