You are presented with the question "starfish lack what kind of system?" and the following answer choices: 
- respiratory
 - critical organs
 - alveoli
 - heat or cold
 - hydration
 - Bodily water
 - food and shelter
 - frontal zones

Now knowing that echinoderms lack respiratory and excretory systems and echinoderms are represented by the starfish, choose the best answer.


 

 respiratory        