Final answer:
The alveoli are not found in the upper respiratory tract; they are located at the end of the bronchial tree in the lower respiratory system. The upper respiratory tract includes the nasal cavity, pharynx, and larynx.
Step-by-step explanation:
The structure that is not found in the upper respiratory tract is D. Alveoli. The upper respiratory tract consists of the nasal cavity, pharynx, and larynx. The trachea serves as a transitional area between the upper and lower respiratory tracts but is often listed as the beginning of the lower respiratory tract because it extends beyond the larynx. The alveoli, however, are definitely a part of the lower respiratory tract. They are small sac-like structures located at the end of the bronchial tree where gas exchange occurs. Specifically, they are found at the end of the bronchioles in the lung tissues.
The correct order through which air passes during inhalation is: B. pharynx → larynx → trachea → bronchi. Air first enters through the nasal cavity or mouth, passes the pharynx, continues through the larynx and the trachea before reaching the bronchi and subsequently the bronchioles and alveoli in the lower respiratory system.