The correct option is C Smoking
Emphysema is a long-term, progressive disease of the lungs that primarily causes shortness of breath due to over-inflation of the alveoli (air sacs in the lung). It is mainly caused because of Smoking. Shortness of breath is the most common symptom of emphysema. A cough, sometimes caused by the production of mucus, and wheezing may also be symptoms of emphysema. Stopping of smoking and bronchodilating medications along with steroid medications are the treatment of this disease. Hence, the correct answer is option C.