smelting ore evaporation of polluted water jet airplane exhaust high in the sky sulfur combining with water vapor in the atmosphere
I gave my students this multiple choice question: What is the MAJOR cause of acid rain?

Only one answer is correct among these 4 choices:
- smelting ore
- evaporation of polluted water
- jet airplane exhaust high in the sky
- sulfur combining with water vapor in the atmosphere

Could you tell me which one is correct?

sulfur combining with water vapor in the atmosphere