You are presented with the question "What can be used for hydration?" and the following answer choices: 
- tree bark
 - leaf
 - fur and fat
 - Heat energy
 - Calcium carbonate
 - tree branch
 - mussels
 - a cactus stem

Now knowing that acactus stem is used for storing water and drink lots of water for hydration, choose the best answer.


 

        a cactus stem 