What is the name of the hollow, semi-flexible tube that carries air to the lungs?

The correct choice is the trachea, which is a crucial component of the respiratory system. It serves as a hollow, semi-flexible tube that connects the larynx to the bronchi, allowing air to flow directly into the lungs. The structure of the trachea is reinforced by cartilage rings that help maintain its open shape while still allowing for some degree of flexibility and movement. This flexibility is important for breathing, as it accommodates changes in pressure and volume within the thoracic cavity during inhalation and exhalation.

In addition to its structural role, the trachea is lined with mucous membranes and cilia, which help trap and move particles and pathogens out of the airway, further protecting the respiratory tract and ensuring that air reaching the lungs is as clean and moist as possible. This combination of structural support, protective mechanisms, and direct airflow function underscores the importance of the trachea in the respiratory process.