During Drug Therapy for Pneumonia,a Female Patient Develops a Superinfection

During drug therapy for pneumonia,a female patient develops a superinfection.She asks the nurse how this could have happened.Which is the nurse's best explanation to the patient?

A) Large doses of antibiotics kill normal flora.
B) The infection has spread from her lungs to the new site of infection.
C) The pneumonia-causing bacteria are resistant to the drugs.
D) She is having an allergic reaction to the antibiotics.