Answer and Explanation
The normal microbiota that harbouring an R plasmid will transmit its R plasmid to the normal microbiota because the normal microbiota does not have R plasmid after transmission of R plasmid its increases the resistance capacity of normal microbiota. This is the significance of normal microbiota that harbours an R PLASMID.
They are different ranks in a taxonomy hierarchy. The genus is more exclusive than the phylum.
Order:
Domain,
Kingdom,
Phylum,
Class,
Order,
Family,
Genus,
Species
C is the most likely answer to this question.
The answer I would choose is c