Final answer:
The main bronchus, trachea, alveoli, and acinus are respiratory structures located in the lungs.
Step-by-step explanation:
The main bronchus, trachea, alveoli, and acinus are all respiratory structures located in the lungs. The trachea is a tube that connects the pharynx to the bronchi. The main bronchus is the first branch off the trachea and it divides into the secondary bronchi, which then further divide into the tertiary bronchi and bronchioles. The alveoli are small, air-filled sacs at the ends of the bronchioles, where gas exchange takes place.