You are presented with the quiz "What can decrease in an environment, and may cause animals to leave?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "if the amount of available food and water decreases in an environment then animals may leave that environment to find food and water" and "food, water and air are the essentials of life on earth". 

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


 

 essentials of life          