Common control strategy for waterborne and airborne diseases Steps:

• Identify cholera as waterborne, spread via contaminated water/food in crowds.
• Identify tuberculosis as airborne, spread via respiratory droplets in close quarters.
• Evaluate strategies: 1 targets water sanitation (cholera-specific), 2 targets ventilation/isolation (TB-specific), 3 addresses overcrowding reduction (affects both transmission modes).
• Select option matching only the shared strategy.

Why D is correct:

• Strategy 3 reduces overcrowding, limiting close contact for TB droplets and shared facilities for cholera contamination, per epidemiology principles of transmission control.

Why the others are wrong:

• A includes 1 and 2, which are disease-specific and ineffective for the other.
• B includes only 1, ignoring TB's airborne nature.
• C includes only 2, ignoring cholera's waterborne path.

Final answer: D