- Burning fossil fuels is a source of air pollution
- Coal is a kind of fossil fuel
- Hence, burning coal is a source of air pollution

- Coal is used for generating heat by burning
- Coal is used to produce electricity by burning in coal-fire power stations
- So, using coal usually requires burning coal

- Burning coal is a source of air pollution
- Using coal usually requires burning coal
- Hence, using coal causes air polluiton

Therefore, using coal causes air polluiton
Which resource when used causes the most pollution?
- Coal is used for generating heat by burning 
- Burning fossil fuels is a source of air pollution 
- Coal is used to produce electricity by burning in coal-fire power stations 
- Coal is a kind of fossil fuel