Question

how does carbon return to the soil? combustion of fossil fuels transpiration by plants respiration by animals decomposition of organic matter

Explanation:

When organic matter such as dead plants and animals decays, the carbon within them is released into the soil. Combustion of fossil fuels releases carbon into the atmosphere. Transpiration by plants is the process of water movement through a plant and its evaporation from aerial parts, not related to carbon - soil return. Respiration by animals releases carbon dioxide into the atmosphere, not directly into the soil.

Answer:

Decomposition of organic matter