The large number of alveoli in lungs improve diffusion by
a. increasing the surface area for diffusion
b. decreasing the distance for diffusion
c. changing the diffusion constant
d. increasing the concentration difference

a. Increasing the surface area for diffusion

Explanation:

When the air is inhaled through the nostrils, the air containing the oxygen the air diffuses inside the alveoli. The alveoli are the tiny sacs where air enters and exchange of gases takes place. From the alveoli the oxygen enters into the blood stream. The oxygen is utilized by the cells for respiration. The increase in network and number of the alveoli will increase the surface area for the diffusion of oxygen and hence, will speed up the respiration process.

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since there are no options posted i'll give you a few examples.

a dolphin's flipper, bird's wing, cat's leg.