The ancient reptile Thrinaxodon, an ancestor of mammals, had skull features suggesting that it had sensory whiskers. If Thrinaxodon had whiskers, it clearly also had hair on other parts of its body, which would have served as insulation that regulated body temperature. Ttherefore, Thrinaxodon was probably warm-blooded, for such insulation would be of little use to a cold-blooded animal. Which one of the following most accurately describes the role played in the argument by the statement that if Thrinaxodon had whiskers, it clearly also had hair on other parts of its body, which would have served as insulation that regulated body temperature? ['It is a premise offered in support of the main conclusion drawn in the argument.', "It is offered as an explanation of the phenomenon described by the argument's main conclusion, but it is not itself used to provide support for that conclusion.", 'It is a premise offered in support of the conclusion that insulation regulating body temperature would be of little use to a coldblooded animal.', 'It is a conclusion for which the claim that Thrinaxodon had skull features suggesting that it had sensory whiskers is offered as support.']