Some strains of the bacterium Streptococcus pyogenes secrete poisonous substances called exotoxins. The genes encoding the exotoxins are thought to have originated in the bacteriophages, which are viruses that infect bacteria.

Which of the following is the most likely mechanism by which the S. pyogenes acquired the ability to produce the exotoxins?

a. Bacteriophages engulfed cellular debris from dead bacteria
b. Bacteriophages in the environment activated bacterial cell division
c. Bacteriophage DNA became integrated in the bacterial chromosome
d. Bacteriophage proteins were absorbed into bacterial cells by endocytosis.