You are presented with the quiz "Thirst is used to make animals realize they need to what?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "thirst is used to make an animal realize that it needs to replenish its bodily water by the body" and "water hydrates the cells". 

So, what's the best answer to the question?


 

      hydrate their cells     