by adding particle pollution by creating a hole in the ozone layer by causing acid precipitation to fall by increasing the levels of carbon dioxide
I gave my students this multiple choice question: How has burning fossil fuels most caused a decline to the quality of air that people breathe?

Only one answer is correct among these 4 choices:
- by adding particle pollution
- by creating a hole in the ozone layer
- by causing acid precipitation to fall
- by increasing the levels of carbon dioxide

Could you tell me which one is correct?

by adding particle pollution