Fact 1: Coal is used to produce electricity by burning in coal-fire power stations.

Fact 2: Swamp vegetation was compressed to form coal.

Given the two facts above, answer the question "what is used to produce electricity by burning in power stations?" with the following options: 
- dried mud
 - small animals
 - heat energy
 - chemical reaction
 - carbon dioxide
 - swamp air
 - hydrogen and oxygen
 - swamp vegetation


 

        swamp vegetation 