You are presented with the question "vertebrates have a complete digestive system and a what?" and the following answer choices: 
- Veins and arteries.
 - lack of backbone
 - bruised brain stem
 - critical organs
 - closed circulatory system
 - incomplete circulatory system
 - characteristics
 - sensory neurons

Now knowing that chordates have a complete digestive system and a closed circulatory system and vertebrates are members of of a larger group, the chordates , choose the best answer.


 

     closed circulatory system    