Which statement about the alveoli is correctly worded as an adaptive feature?

1. An adaptive feature must name a structure and the function it serves. 2. Alveoli are numerous and small, which gives a large surface area relative to volume — the ratio runs surface area to volume, not the reverse. 3. Writing 'volume to surface area' inverts the ratio and states the opposite of what helps diffusion. 4. Saying they are in the lungs so they work properly names a location, not an adaptation. 5. Macrophages are a structure present in alveoli, but engulfing dust is defence, not gaseous exchange. _Source: NECTA ACSEE 2023 Biology 133/1, Question 2: Gaseous Exchange and Respiration_