Key factors in alveolar oxygen diffusion Steps:

• Identify features affecting diffusion per Fick's law: surface area, partial pressure gradient, membrane thickness, and diffusion constant.
• Match to numbered choices: assume 1=pressure gradient, 2=surface area, 3=thin membrane, 4=other (e.g., solubility).
• Select combination including essential elements for O2 movement from alveolus to blood.
• Verify A covers core drivers without extras.

Why A is correct:

• Combines pressure gradient (1), surface area (2), and thin membrane (3), directly enabling efficient O2 diffusion via Fick's law: rate ∝ (area × ΔP) / thickness.

Why the others are wrong:

• B includes 4 (non-essential) but omits 2 (surface area), reducing efficiency.
• C excludes 2 (surface area), limiting total O2 transfer.
• D lacks 1 (gradient) and 3 (thickness), halting diffusion.

Not enough information on exact features 1–4.

Final answer: A