What is the recommended spirometry testing criteria for smokers?

B is the correct choice because spirometry testing is recommended for smokers, particularly those over the age of 35 who experience breathing difficulties. Smokers are at a higher risk for developing chronic obstructive pulmonary disease (COPD) and other respiratory issues, so identifying early signs of lung dysfunction through spirometry can lead to timely intervention and management of any potential respiratory conditions.

In contrast, the age threshold in other options does not align with the guidelines, or the presence of symptoms isn't appropriately considered. For instance, option A mentions smokers with normal breathing patterns, which does not warrant spirometry testing since the primary focus is on those who exhibit breathing difficulties. Option C addresses non-smokers, which does not pertain to the recommended criteria for smokers, and option D suggests testing smokers without any lung issues, which does not align with best practices since testing is typically reserved for those showing symptoms or risk factors.