AS biology help

[Fishface]

Hi, i am stuck on a question in my biology homework. I am currently taking AS biology (just to help you see what level i am at)

So the question is... How does diffusion result in the alveoli having a moist surface

The only answer i can think of (well couple of answers) is that the alveoli have a moist tissue area to make for more efficent diffusion (but this doesn't say why it results in it having a moist surface area)

The only other idea i had was that diffusion is the net movement of moelcules from an area of higher concentration to an area of lower concentration and so maybe the surface area has a lower area of concentration and so the water molecules have diffused there and so the sufrace area becomes moist

Are any of these right or am i going off on a tangent here?

[mith]

I think the moist surface is a requirement of diffusion since you cannot have air to liquid(blood) without some sort of wet interface or you would dry your blood out.