Answer: d. Smoking damages cilia in the trachea and more particles enter the lungs.
Explanation:
Smoke which is swallowed or inhaled by smoking damages the cilia present in the trachea of the respiratory passage. When the cilia becomes ineffective in process of keeping the lungs clear, the smokers may develop a cough in a process to remove the mucus from the lungs. The dirt or dust particles also enters into the respiratory passage due to non functioning of the cilia. The damage of cilia increases the risk of pneumonia and other kind of respiratory infections.
