Final answer:
The biotic, or living, part of soil mentioned in the options is C. microorganisms, which include living organisms that play crucial roles in soil ecology.
C is correct
Step-by-step explanation:
Soil is indeed a living system, comprising both biotic and abiotic factors. Biotic factors include the living aspects of the environment, such as organisms and microorganisms. Abiotic factors, on the other hand, include nonliving aspects like sunlight, soil structure, gases, minerals, and water.
Based on this understanding, the correct answer to which of the following is a biotic, or living, part of the soil is C. microorganisms. Microorganisms are the living creatures that inhabit the soil, and they play a vital role in various ecological processes such as the degradation of organic matter and the biogeochemical cycles.