This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Medicine
[{'content': 'Common cause of obstructive lung disease is \nSelect and explain. \nA. Smoking, B. Air pollution, C. Genetic, D. Occupational', 'role': 'user'}, {'content': 'Answer: A \nExplanation: (A) Smoking > Air pollution, airway infection, familial factors, and allergy have also been implicated in chronic bronchitis, and hereditary factors (deficiency of a 1-antiprotease) have been implicated in emphysema.> The pathogenesis of emphysema may involve excessive lysis of elastin and other structural proteins in the lung matrix by elastase and other proteases derived from lung neutrophils, macrophages, and mononuclear cells.> Atopy and the tendency for bronchoconstriction to develop in response to nonspecific airway stimuli may be important risks for COPD.', 'role': 'assistant'}]