Cigarette smoking causes emphysema. Give reason. 

Explanation

### Step-by-Step Solution:

1. **Understanding Emphysema**: Emphysema is a chronic disorder of the respiratory system characterized by the abnormal distension of the alveolar walls. This leads to a decrease in the surface area available for gas exchange.

2. **Role of Cigarette Smoking**: Cigarette smoking introduces harmful substances and toxins into the lungs. Over time, these substances can cause significant damage to the lung tissues.

3. **Damage to Alveoli**: The inhalation of smoke from cigarettes leads to the destruction of the septa (the walls) between the alveoli. This damage reduces the number of functional alveoli available for gas exchange.

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