A)increasing the surface area of the body
B)increasing the partial pressure of oxygen inside of the cells
C)increasing the thickness of the body wall
D)increasing the surface area of the body and the partial pressure of oxygen inside the cells
E)All of these choices are correct.

A)a large surface area
B)a small surface area
C)a thickness of 100 micrometers
D)a thickness under 10 micrometers

A)Circulation requires a pump to generate pressure to drive flow, whereas ventilation does not.
B)Ventilation increases the concentration of oxygen in the air on the outside of the respiratory surface.
C)The same amount of oxygen enters the blood through diffusion as is transported by circulation.
D)Oxygen and carbon dioxide both move across the respiratory surface by diffusion.
E)Larger, more complex animals rely on bulk flow and diffusion to deliver oxygen to their cells, whereas some smaller, simpler animals rely on diffusion alone.