Pablo and johanna have to do a yearlong study for their biology course. after some discussion, they decide to try comparing their dogs and the diet that they feed them to test their hypothesis that the local veterinarian's special dog food mix will enhance growth and development. each student adopts a puppy from the local pound. pablo plans to feed his shepherd-mix dog the special diet, while johanna plans to use generic dry kibble from the supermarket for her bulldog. the independent variable in this study will be