A 50-year old man has a 30 year history of smoking. For approximately 6 months per year for the preceding 5 years, he has had copious sputum production. This sputum production is most likely closely related to increased numbers of which of the following cell types in his bronchioles and small (less than 3 mm) bronchi?
Goblet cells Smooth muscle cells Squamous cells Type I pneumocytes