Question

what is humus? a type of worm that only lives in the soil mineral matter or pieces of rock in the soil substance from decaying organic material

Explanation:

Humus is formed from the decomposition of organic matter such as dead plants and animals. It is not a type of worm (which would be an organism, not a soil - related substance) or mineral matter/rock pieces (those are inorganic in nature).

Answer:

substance from decaying organic material