Answers

2015-06-30T19:46:01+05:30
They are 
thin, moist membrane (allows gas diffusion) and large surface area (maximizes rates of diffusion).
1. large surface area. There are many alveoli and the shape allows for a high surface area. This is significant because it allows gas exchange to occur simultaneously over a large area. 

2. high concentration of red blood cells. This allows for easy transport of oxygen and carbon dioxide since all the cells are simultaneously carrying these gases.
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