Correct Answer: B
Explanation:
The trachea and bronchi have cartilage rings or plates in their walls that allow them to stay open despite changes in intrapleural pressure. The bronchioles have no cartilage and may collapse when the intrapulmonary pressure exceeds the pressure in the airway. The principal sites of airways resistance are the upper airways (mainly the nose and airway generations 1-6). While the alveoli are the principal site of gas exchange, the respiratory bronchioles and alveolar ducts also contribute.