Where does the organic material in soil originate?
a. physical weathering
b. chemical weathering
c. decomposing plant and animal matter
d. the atmosphere

The answer is letter C.

Almost all of the organic materials found in soil come from decomposing plant and animal matter. These organisms that undergo decomposition contribute to the soil's organic compounds. Their cells and tissues breakdown and assimilate with the soil which heightens the soil's chemical compounds and overall good quality.