Answer:D
Explanation: Protozoans are a single-celled microscopic animal of a group of phyla of the kingdom Protista, such as an amoeba, flagellate, ciliate, or sporozoan.
Protozoans play important roles in the fertility of soils. By grazing on soil bacteria, they regulate bacterial populations and maintain them in a state of physiological youth— in the active growing phase. This enhances the rates at which bacteria decompose dead organic matter.
