Respiratory structures with cartilage and cilia

Steps:

• Identify cartilage as supportive rings in larger airways like trachea and bronchi.
• Recognize cilia as motile projections in epithelial linings for clearing mucus in conducting airways.
• Examine structure 1 (trachea): contains C-shaped cartilage rings and ciliated pseudostratified epithelium.
• Examine structures 2 (alveoli) and 3 (bronchi): alveoli lack both, while bronchi have cartilage plates and cilia.

Why C is correct:

• Trachea (1) and bronchi (3) both feature cartilage for rigidity and cilia for mucociliary transport, per standard respiratory anatomy.

Why the others are wrong:

• A includes 2 (alveoli), which have neither cartilage nor cilia.
• B omits 3 (bronchi), which contain both features.
• D excludes 1 (trachea), which has both cartilage rings and cilia.

Final answer: C