How did some strains of Staphylococcus aureus become resistant to antibiotic drugs?

• A. The drug did not work in the way that the developers intended.
• B. Patients did not take the drug as it was prescribed.
• C. The bacterium mutated in response to the drug.
• D. None of the listed responses is correct.
• E. Some members of the bacteria population must have had genetic variation that made them resistant to antibiotics, and these bacteria had greater reproductive success than sensitive individuals.