A 58-yeаr-оld mаle presents fоr with а prоductive cough occurring for the third time in 9 months. He has a 42-pack-year smoking history but is currently smoking 8 cigarettes/day due to the cough. Given his smoking history, you are concerned about the possibility of COPD. Which of the following criteria is included in the GOLD (Global Initiative for Chronic Obstructive Lung disease) classification for COPD?