A recent study concludes that prehistoric birds, unlike modern birds, were cold-blooded. This challenges a widely held view that modern birds descended from warm-blooded birds. The conclusion is based on the existence of growth rings in prehistoric birds' bodily structures, which are thought to be found only in cold-blooded animals. Another study, however, disputes this view. It concludes that prehistoric birds had dense blood vessels in their bones, which suggests that they were active creatures and ttherefore had to be warm-blooded. Which one of the following, if true, would most help to resolve the dispute described above in favor of one party to it? ['In some cold-blooded species the gene that is responsible for growth rings is also responsible for dense blood vessels.', 'Dense blood vessels are not found in all warm- blooded species.', 'Having growth rings is not the only physical trait of cold-blooded species.', 'Modern birds did not evolve from prehistoric species of birds.']