Which of the following is not a way that humus affects the properties of soil?
a. humus expands with increased moisture levels.
b. humus increases the movement of water and air in soil.
c. humus decreases the porosity of soil.
d. humus acts as the basis for soil life.

The question says,'which of the following is not a way that humus affect the properties of the soil. The correct option is C. Humus is the organic constituent of the soil formed by the decomposition of plant materials by soil microbes. Humus is very important in the soil, for it is largely responsible for how fertile a soil is. One of the benefits of humus to the soil is that it increases the porosity of the soil, thereby allowing water and air to pass through the soil easily.