The figure above shows plates made from a culture growing bacteria during specified generations. The culture has white and dark bacteria. After generation 1, scientists applied an experimental drug intended to kill the bacteria and kept the experimental drug in the culture during successive generations. Which statement best explains the results of the experiment? A. The white bacteria showed resistance to the drug. B. Both the dark and the white bacteria showed equal resistance to the drug. C. The drug had no effect on the population. D. The dark bacteria showed resistance to the drug.