One criticism of these experiments might be that the presence of more than one sample of bacteria in each Petri dish might have had an effect on the results. Which of the following changes in experimental design could be made to counter this criticism?
F. Use additional species of bacteria in each test.
G. Use only bacteria that was taken directly from nature and not generated in a lab.
H. Place each sample in a separate Petri dish.
J. Vary the size of the starting sample.