In the late 1980s and early 1990s,the percentage of Icelandic children whose bacterial infections were caused by bacteria resistant to penicillin rose at an alarming rate.After public health officials initiated a campaign to reduce the use of penicillin,resistance dropped off.(See the accompanying figure.)
This observation is consistent with the hypothesis that ________.

A) bacteria generate mutations so that they can evolve in order to become better adapted to their environment
B) the use of antibiotics generates mutations in bacteria that affects their resistance
C) antibiotics really have no effect on bacterial resistance; such fluctuations are natural and occur whether we use antibiotics or not
D) bacterial populations evolve in response to the selection pressure imposed by antibiotics