Final answer:
The smallest conducting passageways in the lungs are the terminal bronchioles, which lead to the respiratory zone where gas exchange occurs in the alveoli.
Step-by-step explanation:
The smallest conducting passageways of the lungs are the terminal bronchioles. These bronchioles are the last part of the conducting zone before the respiratory zone, which includes the alveolar ducts, alveolar sacs, and alveoli. The terminal bronchioles, which are less than 1 mm in diameter, do not contain cartilage like the larger bronchi do. Instead, their walls are made of smooth muscle that can adjust their diameter to regulate airflow in the lungs. Each lung contains more than 1000 terminal bronchioles that lead to the structures where gas exchange occurs, namely the alveolar sacs that hold clusters of alveoli.
It's important to note that while the alveoli are the sites of gas exchange, they are not considered part of the conducting airways, as they are involved in the respiratory zone, not the actual passage of air. Therefore, Letter C) "terminal bronchioles" is the correct answer.