Alveoli lack cilia but have thin, moist walls for gas exchange

Steps:

• Recall alveoli structure: air sacs in lungs lined by simple squamous epithelium.
• Identify key features: walls are one cell thick and moist to facilitate diffusion; no cilia present.
• Evaluate choices: A suggests cilia (incorrect); B and C mix yes/no inaccurately; D correctly indicates absences and presences via x/no.
• Confirm D matches biology: no cilia, yes moist/thin walls.

Why D is correct:

• Alveoli walls are one cell thick (simple squamous) per respiratory physiology, enabling efficient O2/CO2 diffusion; D's "x / x x no" aligns with no cilia but yes for moist/thin traits.

Why the others are wrong:

• A incorrectly claims cilia lining, which occurs in trachea, not alveoli.
• B wrongly affirms only one feature (likely moist) while ignoring thin walls.
• C denies a key yes (moist or thin), violating gas exchange requirements.

Final answer: D