Answer:
Combustion,respiration
Step-by-step explanation:
Carbon is the major element in the dry matter of all living things. Respiration by both plants and animals converts some of the organic compounds into carbon dioxide. The latter is released to the atmosphere and reused by green plants.
When plants and animals die, their carbon compounds are converted into carbon dioxide by the action of saprophytic bacteria and fungi. The carbon dioxide is released back to the atmosphere.
When coal, natural gas and oil are combusted as fuels they release carbon dioxide to the atmosphere.