When penicillin was first introduced, it was effective in destroying most of the bacteria that cause gonorrhea. Today, certain varieties of this bacterium are resistant to penicillin. Which statement best explains the appearance of these resistant varieties?
a
Penicillin stimulated the bacteria to become resistant, and the resistance was passed to the offspring.
b
Penicillin stimulated the production of antigens in the resistant bacteria.
c
Penicillin used today is not as strong as the penicillin used when it was first introduced.
d
Penicillin killed the susceptible bacteria, and naturally resistant variations survived to reproduce.
d
Penicillin killed the susceptible bacteria, and naturally resistant variations survived to reproduce.