D I believe that’s the answer
Diffusion is the random movement of molecules or particles from a region of high concentration to a region of low concentration bringing a natural flow in the system. Diffusion ensures that there is a state of equilibrium in the number of molecules in the system.
the first answer as blood needs to be oxygenated to be passes round the body then when its deoxgenated it will return to the heart to be pumped around the body again
