Name the pulmonary disease in which the alveolar surface area involved in gas exchange is drastically reduced due to damage to the alveolar walls.

a) Asthma is an allergic disorder in which bronchioles constrict due to spasm of smooth muscles and the expiration becomes difficult.
b) Pleurisy is inflammation of pleural membranes. There is an accumulation of fluid between the pleural membranes. This results in a sharp chest pain and breathing become difficult.
c) Emphysema is a disorder of respiratory system in which there is irreversible distension of the respiratory bronchioles, alveolar sacs and alveoli. The wall separating adjacent alveoli break down and the air remains filled even after expiration. Smoking causes inflammation of lung alveoli which results in a decrease in surface area for gaseous exchange and causes emphysema.
d) Pneumonia is a disease of lungs which is characterised by inflammation of lungs and accumulation of mucus in alveoli and bronchioles that make breathing quite difficult.
So, the correct answer is C.