waste acid from chemical factories being pumped into rivers acid from chemical laboratories evaporating into the air gases from burning coal and oil dissolving in water in the atmosphere gases from air conditioners and refrigerators escaping into the atmosphere
I gave my students this multiple choice question: One of the principal causes of acid rain is

Only one answer is correct among these 4 choices:
- waste acid from chemical factories being pumped into rivers
- acid from chemical laboratories evaporating into the air
- gases from burning coal and oil dissolving in water in the atmosphere
- gases from air conditioners and refrigerators escaping into the atmosphere

Could you tell me which one is correct?

gases from burning coal and oil dissolving in water in the atmosphere