What term describes the main passageway for air to enter the lungs?

The term that describes the main passageway for air to enter the lungs is "trachea." The trachea, commonly known as the windpipe, is a tube that extends from the larynx (voice box) down into the thoracic cavity, branching into the left and right bronchi that lead into each lung. Its primary function is to provide a clear airway for air to enter and exit the lungs during respiration.

The structure of the trachea is designed for efficient air transport; it consists of C-shaped cartilaginous rings that keep it open to prevent collapse. Additionally, the trachea is lined with mucous membranes and cilia, which help trap and move particles and pathogens upwards, away from the lungs.

The other terms listed refer to structures associated with the respiratory system but serve different functions. Bronchi are the two main branches the trachea splits into, leading into the lungs. Alveoli are tiny air sacs in the lungs where gas exchange occurs. Pleura refers to the membranes surrounding the lungs, which facilitate movement during breathing but do not function as an airway. Therefore, "trachea" is the correct term for the primary pathway for air entering the lungs.