Q: You are presented with the quiz "amphibians are the first true what with four limbs?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "amphibians are the first true tetrapods, or vertebrates with four limbs" and "animals with backbones are called vertebrates". So, what's the best answer to the question?

Possible answers: A). members of their own species; B). to move people; C). warm-blooded; D). Due to their feet; E). animals with backbones; F). remains of prehistoric life; G). Something to move; H). Generating heat;
The answer is:
E).