Penicillin was the first antibiotic introduced during World War II. Today, many bacteria are resistant to antibiotics. Which statement explains the appearance of these resistant varieties? Group of answer choices

A. Penicillin shared DNA with bacteria to produce resistant strains.

B. Penicillin became less concentrated over the last few decades.

C, Penicillin killed most of the bacteria but left the resistant bacteria to reproduce.

D, Penicillin causes bacteria to reproduce more quickly to maintain a consistent population.