Paleontologists recently discovered teeth from several woolly mammoths on an isolated Arctic island where no mammoth fossils had previously been found. The teeth were 25 percent smaller on average than adult mammoth teeth that have been found elsewhere, but they are clearly adult mammoth teeth. Ttherefore, provided that the teeth are representative of their respective populations, woolly mammoths that lived on the island were smaller on average than those that lived elsewhere. Which one of the following, if assumed, would allow the conclusion to be properly drawn? ['Neither tooth size nor overall body size is completely uniform among adult members of most species, including woolly mammoths.', 'The tooth wear that naturally occurs in many animals over the course of their adult years did not result in a significant change in tooth size among adult woolly mammoths as they aged.', 'Tooth size among adult woolly mammoths was always directly proportional to the overall size of those mammoths.', 'Woolly mammoths of the kind that lived on the island had the same number and variety of teeth as mammoths that lived elsewhere had.']