Fact 1: Air pollution harms the respiratory and circulatory systems.

Fact 2: Nitrogen oxides cause air pollution.

Given the two facts above, answer the question "Harm to the respiratory and circulatory systems can come from " with the following options: 
- Greenhouse gases
 - hydrocarbons
 - Sulfur dioxide
 - nitrogen oxides
 - burning coal
 - fossil fuels
 - emissions
 - Greenhouse gasses


 

    nitrogen oxides     