Which one of the following characteristics would you expect to find in alveoli to make them efficient at gas exchange?Small surface areaThick wallsRich supply of blood capillariesLong diffusion distance

The characteristic that makes alveoli efficient at gas exchange is a "Rich supply of blood capillaries".

Here's why:

1. Small Surface Area: This would actually make gas exchange less efficient. The larger the surface area, the more space there is for gas exchange to occur.

2. Thick Walls: This would also make gas exchange less efficient. The thinner the walls, the shorter the distance oxygen and carbon dioxide have to travel to move between the alveoli and the blood.

3. Rich Supply of Blood Capillaries: This is correct. A rich supply of blood capillaries around the alveoli allows for a greater amount of blood to come into close contact with the alveoli, facilitating efficient gas exchange.

4. Long Diffusion Distance: This would make gas exchange less efficient. The shorter the diffusion distance, the faster the rate of gas exchange.