As the bronchial tree terminates in bronchioles, the principal material comprising their walls is smooth muscle. What functional purpose does this smooth muscle provide?
a. The walls of the bronchioles provide patent airways to the alveoli.
b. The walls of the bronchioles allow for gas exchange before air actually enters the alveoli.
c. The presence of smooth muscle allows the walls of the bronchioles to constrict and provides control over air flow.
d. Both a and c are true.
Answer: C
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