smelting ore evaporation of polluted water jet airplane exhaust high in the sky sulfur combining with water vapor in the atmosphere
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: What is the MAJOR cause of acid rain?
Possibilities:
- smelting ore
- evaporation of polluted water
- jet airplane exhaust high in the sky
- sulfur combining with water vapor in the atmosphere

sulfur combining with water vapor in the atmosphere