Question

what does humus contribute to soil? it prevents water from entering the soil. it kills off living organisms. it enriches organic matter.

Explanation:

Humus is decomposed organic material. It adds nutrients to the soil, which enriches the organic matter. It does not prevent water (it can actually help with water retention in some cases) and it does not kill organisms (many organisms help create humus).

Answer:

It enriches organic matter.