Between A and B

Hi @Anna The conclusion is that Thrinaxodon was probably warm-blooded, and the statement that “for such insulation would be of little use to a cold-blooded animal” is offered as support for that conclusion. The indicator word “for” signals this support, and the “therefore” signals the conclusion. That is why answer B is correct — answer A is wrong because the conclusion is not that insulation regulating body temperature would be of little use to a cold-blooded animal. Notice that A does not phrase it as you to, with the linkage back to Thrinaxodon probably being warm blooded. The answer merely says what it says — just the logic supporting the conclusion. I hope that helps! Please let us know if you have further questions.