You are presented with the quiz "vertebrates have a complete digestive system and a what?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "chordates have a complete digestive system and a closed circulatory system" and "vertebrates are members of of a larger group, the chordates ". 

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


 

     closed circulatory system      