What structures make up the lower airway?

The correct answer encompasses the complete anatomical structures that comprise the lower airway in the respiratory system. The trachea serves as the main airway that branches into the bronchi, which further divide into bronchioles—these smaller tubes are critical for directing air to the alveoli, the tiny air sacs where gas exchange occurs. Each of these components plays a fundamental role in ensuring effective respiration, starting with the trachea that conducts air toward the lungs and culminating in the alveoli where oxygen and carbon dioxide are exchanged.

In the context of the other options, while the pharynx and larynx are important parts of the upper airway, they do not belong to the lower airway. The second option incorrectly mixes components from different parts of the respiratory system. The third option mentions the lungs and alveoli, but lacks the inclusion of the trachea and bronchi, which are essential for the pathway of air into the lungs. Finally, the fourth option includes the diaphragm, which is a muscular structure that assists in breathing but does not constitute part of the airway itself. Therefore, the most comprehensive and correct choice includes all relevant structures associated with the lower airway.