In experiments in which certain kinds of bacteria were placed in a generous supply of nutrients, the populations of bacteria grew rapidly, and genetic mutations occurred at random in the populations. These experiments show that all genetic mutation is random. Which one of the following, if true, enables the conclusion to be properly drawn? ['The nutrients used were the same as those that nourish the bacteria in nature.', 'Either all genetic mutations are random or none are random.', 'The kind of environment in which genetic mutation takes place has no effect on the way genetic mutation occurs.', 'The bacteria tested in the experiments were of extremely common forms.']