Answer:
The correct answer would be the carbon cycle.
Fossil fuels, decomposers, plants, and animals are all parts of the carbon cycle.
Decomposers breakdown the dead animals and plants into simpler compounds and help in returning the nutrients back to the environment.
These dead and decayed animals and plants, when buried for millions of years, get converted into fossil fuels due to high temperature and pressure.
Fossil fuels like coal, petrol et cetera release carbon into the atmosphere in the form of carbon dioxide when they are oxidized in automobiles and factories.