Final answer:
The respiratory system structures relevant to the question are the trachea and bronchi. The thymus is not part of the respiratory system. The correct pathway of air during inhalation is nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli.
Step-by-step explanation:
The respiratory system structures include the trachea, bronchi, and other organs and pathways involved in the intake and exchange of oxygen and carbon dioxide. The thymus, while located in the chest, is not part of the respiratory system but rather is involved with the immune system. Therefore, the correct answer to the question 'Which of the following are respiratory system structures? a. thymus b. trachea c. bronchi d. All of the above' would be both b. trachea and c. bronchi, making d. All of the above incorrect.
During inhalation, air follows the pathway: nasal cavity, pharynx, larynx, trachea, bronchi, and finally bronchioles, before reaching the alveoli for gas exchange. The conducting zone of the respiratory system includes structures through which air travels to reach the lungs such as the nasal cavity, pharynx, trachea, bronchi, and most bronchioles. The respiratory zone is where the actual gas exchange occurs, involving the terminal bronchioles and alveoli.