The Bacterium Staphylococcus Aureus Is Commonly Found in the Nasal

The bacterium Staphylococcus aureus is commonly found in the nasal cavity of healthy people. If inhaled into the lungs, however, it may cause pneumonia. Staphylococcus aureus is best described as

A) a parasite.
B) resident microbiota.
C) a mutualist symbiotic partner.
D) transient microbiota.
E) both resident microbiota and opportunistic pathogen.