Fact 1: Chordates have a complete digestive system and a closed circulatory system.

Fact 2: Because reptiles are vertebrates, they are chordates.

Given the two facts above, answer the question "vertebrates have a complete digestive system and a closed what?" with the following options: 
- digestive tract
 - lung system
 - the body's largest organ
 - circulatory system
 - Veins and arteries.
 - brain stem
 - all liquids
 - major threat to health


 

    circulatory system     