Answer:
Resident microflora b. may be responsible for opportunistic infections in immunocompromised
Explanation:
It is almost impossible to found these microorganisms in the stomach because of the acidic conditions, most of them are not adapted to this type of environment. Resident microflora is not transient, is actually permanent. However, resident microflora may be responsible for ooportunistic infections in immunocompromised and they can also increase the intensity of the disease produced by that pathogen.
Population is the answer !
The answer is, "B", "Sugars".
The branch of biology dealing with interactions along organisms and between organisms and their environment is called Ecology, I believe.