Maximum surface area of circulating system isnseen in which one of these?

a-heart

b--capillaries

c-arterioles

d-veins

If you are asking for the maximum surface area among different components of circulatory system  then correct answer is capillaries. Huge network of capillaries contribute maximum to the surface area of  total blood vessels in the body. 

Hence, the correct answer is b) Capillaries