What is the main function of the trachea in the respiratory system?

The correct answer highlights the primary role of the trachea as a passage for air to reach the lungs. The trachea is a tubular structure that connects the larynx (or voice box) to the bronchi, which branch into the lungs. Its main function is to conduct air in and out of the respiratory system. The trachea is lined with cilia and mucus, which help to trap particles and pathogens, ensuring that the air reaching the lungs is clean and free of debris.

The other choices refer to functions that do not accurately represent the main role of the trachea. Division into larger bronchi pertains to the branching of the trachea and occurs further along in the airway pathway, while protection of the lungs is a broader role involving several structures in the respiratory system, including the rib cage and pleura, rather than the trachea itself. Lastly, while the trachea is involved in phonation due to its connection to the larynx, sound production is predominantly a function of the vocal cords rather than the trachea's main function.