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

Fact 2: Coal-fired power stations are inherently modular.

Given the two facts above, answer the question "coal is used to produce electricity by burning in inherently modular what?" with the following options: 
- heat
 - stations
 - trees
 - heat energy
 - similar
 - cells
 - adding heat
 - engines


 

  stations       