You are presented with the question "What causes an  animal population to decrease?" and the following answer choices: 
- sound pollution
 - Greenhouse gases
 - Pesticides
 - water
 - fossil fuels
 - Air pollution
 - animal diversity
 - steroids

Now knowing that harming an animal species causes that animal 's population to decrease and air pollution also harms plants and animals, choose the best answer.


 

      Air pollution   