Final answer:
The bronchioles contain a layer of smooth muscle and are the correct answer for the presence of smooth muscle in their structure, whereas the alveoli do not contain smooth muscle.
Step-by-step explanation:
The bronchi and bronchioles both contain layers of smooth muscle in their walls. As the airways in the lungs branch out from the trachea, they form the bronchi and subsequently the bronchioles. The bronchi are made of cartilage and smooth muscle, and as they continue to divide and become smaller in diameter, they form bronchioles which have more prominent smooth muscle in their composition and lack cartilage. The alveoli, on the other hand, do not contain smooth muscle; their primary function is gas exchange, and they have thin walls to facilitate this process.
C. Bronchioles contain a layer of smooth muscle; they are air passages smaller than 1 mm in diameter that extend from the bronchi and are made of smooth muscle and elastic fibers.