You are presented with the quiz "The first true tetrapods, or vertebrates with four limbs include" 

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 "frogs are amphibians and ducks are aves". 

So, what's the best answer to the question?


 

  frogs         