You are presented with the question "Frogs have a _-chambered heart." and the following answer choices: 
- alveoli
 - organ
 - ovaries
 - oxygen
 - edible
 - three
 - nektar
 - CO 2

Now knowing that amphibians have a relatively complex circulatory system with a three-chambered heart and all frogs are amphibians, choose the best answer.


 

      three   