You are presented with the question "Escaping poor weather and food supply changes what?" and the following answer choices: 
- population age
 - the environment
 - population education
 - general preferences
 - important habitats
 - population size
 - movement
 - an organism's body

Now knowing that migration is a type of movement that changes population size and birds migrate to escape poor weather and food supply, choose the best answer.


 

      population size   