The many branches leading into the human lungs become smaller until they end in small sacs called alveoli. Each alveolus is surrounded by a net of tiny capillaries.
How does the finely branched structure of the capillary nets relate to their function in the respiratory system?
A. The branching capillaries allow the flowing blood to warm all of the surfaces of the alveoli.

B. The branching capillaries attach to the walls of the alveoli to keep them expanded and full of air.

c The branching capillaries Join bundles of alveoll together and keep them separated from other bundies.

D. The branching capillaries provide many points where the capillaries and alveoli touch and exchange gases.