Fact 1: Thirst is used to make an animal realize that it needs to replenish its bodily water by the body.

Fact 2: An example is H2O which shows water is made of two atoms of hydrogen stuck to one atom of oxygen.

Given the two facts above, answer the question "Thirst shows an animal that it needs what?" with the following options: 
- CO2
 - H2O
 - He
 - food
 - feed
 - urea
 - O2
 - H20


 

  H2O       