<prompt> 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?Alveolar ductAlveolar sacBronchioleBronchus  <response>: 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. 