Which of the following is an organic material that forms in soil when plant and animal matter decays?

Humus is a dark, organic material formed by the decomposition of plant and animal matter in the soil. It is an essential component of healthy soil because it benefits plants and soil fertility.

Humus is formed by microorganisms such as bacteria and fungi decomposing plant and animal matter. As these microorganisms decompose organic matter, they release nutrients into the soil that plants can use. 

It also helps to improve soil structure by increasing the soil's water-holding capacity and nutrient retention.