Very aggressive pathogens such as the bacterium responsible for tuberculosis can easily overwhelm the protective features of the respiratory system. less aggressive pathogens may be stopped by all of the following except
a. alveolar macrophages
b. air filtration in the nasal cavity
c. the olfactory epithelium
d. the mucus film lining much of the respiratory tract.

C. the olfactory epithelium

Explanation:

According to various studies conducted by medical professionals it can be said that all of the answers provided except for the olfactory epithelium can stop less aggressive pathogens. This is because the olfactory epithelium is a tissue inside the nasal cavity whose only purpose is to send odor signals to the brain, but does not contain anything that can stop less aggressive pathogens.

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for respect usually. some people might be little awkward if you meet or some would be different. usually   you dont love people when you meet them depends on the type of person.

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d they all are treatable but they never completely go away