In Florey and Chain’s experiment, eight mice were infected with lethal doses of Streptococcus bacteria. The four mice given penicillin survived, but the untreated mice died. What can be concluded from these results?

A. The experiment should be repeated with more mice.
B. There is a causal relationship between the use of penicillin and antibiotic resistance in bacteria.
C. Penicillin can be used to treat bacterial infections in humans.
D. Penicillin may have played a role in the recovery of the four mice.

D