You are presented with the question "How do echinoderms use their feet to locomote themselves?" and the following answer choices: 
- one at a time
 - to move people
 - running and lifting
 - protein channels
 - a hydraulic system
 - it needs them
 - undulations
 - It helps them survive

Now knowing that echinoderms have a unique water vascular system with tube feet and echinoderms have a hydraulic system of locomotion called the water vascular system, choose the best answer.


 

     a hydraulic system    