Why is it that bronchioles can constrict and so reduce their diameter while sec- ondary bronchi and respiratory bronchioles cannot constrict? A. Bronchioles have smooth muscle but no cartilage in their walls while sec- ondary bronchi are supported by cartilage. B. Bronchioles have smooth muscle but no cartilage in their walls while respi- ratory bronchioles are supported by cartilage. C. Bronchioles have cartilage but no smooth muscle in their walls while sec- ondary bronchi are supported by cartilage. D. Bronchioles have cartilage but no smooth muscle in their walls while respi- ratory bronchioles only have smooth muscle in their walls.
Option A. Because bronchioles have smooth muscle but no cartilage in their walls while sec- ondary bronchi are supported by cartilage.
