Answer
b. humus
Work Step by Step
Humus is the decaying organic material found in soil. Plants thrive in loams, which are soils that have equal amounts of sand, clay, and silt, but plants also need humus for the nutrients it contains, its ability to hold onto positively charged minerals, and the way it opens up holes for air to squeeze through. Between 10 and 20 percent of humus in the soil is best for most plants.
