The correct option is A Emphysema: reduction of surface area of alveoli and bronchi
Emphysema is a condition that arises in smokers where terminal bronchioles get obstructed. Many alveoli coalesce together to form large chambers due to destruction of their walls, reducing the area of alveolar surface across which gases are exchanged. All these changes reduce both oxygen uptake and carbon dioxide elimination.
Pneumonia is an infection that inflames the air sacs in one or both lungs. The air sacs may fill with fluid causing cough, fever, chills, and difficulty in breathing.
Silicosis is a lung disease caused when we breathe in dust that contains silica. It causes difficulty in breathing as deposition of silicon takes place in the lungs and beathing passages.
Asthma is a condition in which your airways narrow and swell and produce extra mucus. It causes difficulty in breathing, shortness of breath, etc.