Which of the following are structures of the respiratory system?

The structures of the respiratory system are primarily involved in the process of breathing and gas exchange. The trachea and bronchi are essential components of this system. The trachea, also known as the windpipe, serves as the main airway that conducts air between the larynx and the bronchi, which are the two primary branches that lead into the lungs. The bronchi further branch into smaller tubes called bronchioles that lead to the alveoli, where actual gas exchange occurs.

In contrast, the thymus is part of the immune system and is involved in the development of T-cells rather than any respiratory function. This distinction underscores why the combination of trachea and bronchi is the correct choice; they are integral to the function and anatomy of the respiratory pathway.