If amphibians are the first true animals with backbones with four limbs, then amphibians are the first true what with four limbs?

Answer choices:
- members of their own species
 - to move people
 - warm-blooded
 - Due to their feet
 - animals with backbones
 - remains of prehistoric life
 - Something to move
 - Generating heat

 

     animals with backbones     