Cilia, which resemble hair-like projections, line the bronchus in the lungs and move microbes and debris up and out of the airways. What happens to the cilia in the respiratory tract if a person is a chronic smoker?

• A. The cilia become paralyzed and eventually die from tobacco smoke.
• B. Smokers are more likely to develop more cilia.
• C. The cilia become more active and dense from the tobacco smoke.
• D. Tobacco has no effect on cilia.

Answer: (A)