At the lungs.? A. both oxygen and carbon dioxide diffuse from the alveoli into the blood.
B. both oxygen and carbon dioxide diffuse from the blood into the alveoli.
C. oxygen diffuses into the blood and carbon dioxide diffuses into the alveoli.
D. carbon dioxide diffuses into the blood and oxygen diffuses into the alveoli.

At the lungs, oxygen diffuses into the blood and carbon dioxide diffuses into the alveoli.  

•At the time of exchange of gases, oxygen moves from the lungs to the bloodstream.  

•At similar time, carbon dioxide passes into the lungs from the blood.  

•This takes place in the lungs between the network of tiny blood vessels known as capillaries and the alveoli.  

•The molecules of the oxygen gas combines with the red blood cells that mediates back to the heart.  

•The diffusion of carbon dioxide takes place out of the bloodstream, via the capillaries, and into the alveoli from where it is exhaled out.  

•At the same time, oxygen combines simultaneously with hemoglobin and is carried back to the tissues.  

Thus, the correct answer is option C.

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C.

Explanation:

It can not be A. because if both oxygen and carbon dioxide diffused from the alveoli into the blood there would be too little oxygen and too much carbon dioxide.

If both oxygen and carbon dioxide diffused into the alveoli like in B. then that is even worse than the first one because that would leave our blood without oxygen that our body needs for functioning.

And D. can't be true because we don't run on CO2 but on O2 and getting rid of O2 for CO2 would kill us.