Cilia's primary role in mucus clearance

Steps:

• Identify cilia as hair-like structures on respiratory epithelial cells.
• Recall that cilia beat rhythmically to propel substances.
• Distinguish cilia's movement function from mucus's trapping role.
• Evaluate options against respiratory physiology definitions.

Why A is correct:

• Cilia function to waft mucus upward from airways to throat, preventing blockages, as defined in respiratory tract defense mechanisms.

Why the others are wrong:

• B: Trapping dust and particles is the role of sticky mucus secretions, not cilia.
• C: Cilia do not trap; they only move mucus that traps particles.
• D: Increasing surface area occurs via alveolar walls and folds, unrelated to cilia.

Final answer: A