An efficient gas exchange system needs a large surface area and a short diffusion distance. Which row shows correctly how alveoli are adapted to satisfy these requirements?
- Alarge surface area: elastin fibres prevent the alveolus wall from collapsing; short diffusion distance: an extracellular layer inside the alveolus wall contains blood capillaries
- Blarge surface area: gases dissolve in a layer of liquid to speed up diffusion; short diffusion distance: alveolar walls are next to capillaries
- Clarge surface area: alveoli are folded and interconnected; short diffusion distance: walls of alveoli are only one cell thick
- Dlarge surface area: walls of alveoli are formed of squamous epithelial cells; short diffusion distance: red blood cells are very close to capillary walls