Respiratory System: The Path of Airflow - Bronchioles

The correct answer is the bronchioles.

The respiratory system is the pathway through which air travels to and from the lungs. Inhaled air enters the body through the nose or mouth and then travels down the trachea. The trachea branches into two bronchi, which enter the lungs. The bronchi then divide into smaller and smaller branches called bronchioles. The bronchioles are the smallest airways in the lungs and are where the exchange of oxygen and carbon dioxide occurs.