You are presented with the question "vertebrates have a complete digestive system and a closed what?" and the following answer choices: 
- digestive tract
 - lung system
 - the body's largest organ
 - circulatory system
 - Veins and arteries.
 - brain stem
 - all liquids
 - major threat to health

Now knowing that chordates have a complete digestive system and a closed circulatory system and because reptiles are vertebrates, they are chordates, choose the best answer.


 

    circulatory system     