Answer:
im,not for sure but I think it's B
Explanation:
Add the diagram to your question and I can probably get it for sure
Ventilation systems are needed in a <span>multicellular organism to actually obtain oxygen and give out carbon dioxide. Without this ventilation system, it would be very difficult for multicellular organisms to survive. It has been also observed that surface diffusion is not enough for a multicellular organism to breath.</span>
It depends on the concentration of nerve receptors in different areas of the skin.