I think the answer is natural selection
Answer: Your friend could have Pneumonia or Bronchitis
Explanation: The symptoms for Pneumonia and Bronchitis both include being short of breath and having a cough
The given blank can be filled with gas exchange.
In the mentioned diagram, the magnified structure shown is of alveoli. Alveoli are an essential component of the respiratory system that functions to exchange the molecules of carbon dioxide and oxygen to and from the bloodstream. These are the tiny-balloon configured air sacs situated at the very terminal of the respiratory tree and are aligned in groups all through the lungs.
