You are presented with the question "Harm to the respiratory and circulatory systems can come from " and the following answer choices: 
- Greenhouse gases
 - hydrocarbons
 - Sulfur dioxide
 - nitrogen oxides
 - burning coal
 - fossil fuels
 - emissions
 - Greenhouse gasses

Now knowing that air pollution harms the respiratory and circulatory systems and nitrogen oxides cause air pollution, choose the best answer.


 

    nitrogen oxides     