Smoking as Primary Lung Disease Risk

Steps:

• Identify lung diseases like COPD, emphysema, and cancer, often caused by irritants.
• Evaluate options for direct lung exposure to harmful substances.
• Compare risks: focus on inhalation vs. other routes.
• Select the option with strongest, most common link to lung damage.

Why D is correct:

• Smoking cigarettes delivers tar, nicotine, and carcinogens directly to lungs via inhalation, causing chronic inflammation and cellular damage per medical definitions of tobacco-induced respiratory diseases.

Why the others are wrong:

• A: Antibiotics target infections but overuse leads to resistance, not direct lung disease.
• B: Excessive alcohol harms liver and brain primarily; lung effects are secondary via aspiration, not most likely cause.
• C: Heroin injection risks bloodstream infections or overdose, but lung disease stems more from adulterants or secondary pneumonia, not the act itself.

Final answer: D