You are presented with the question "What do Echinoderms lack?" and the following answer choices: 
- Lungs
 - Mass
 - oxygen
 - eardrum
 - gills
 - ovaries
 - Organs
 - Bodies

Now knowing that echinoderms lack respiratory and excretory systems and lung mechanics and gas exchange are topics during study of the respiratory system, choose the best answer.


 

 Lungs        