Which of the following is NOT a main component of soil?

The correct choice identifies rocks as not being a main component of soil. Soil is typically composed of four primary components: mineral matter, organic matter, water, and air. Mineral matter consists of tiny particles derived from the weathering of rocks, which contributes to the soil's structure and nutrient content. Organic matter includes decomposed plant and animal materials, which enrich the soil and support microbial life.

While rocks are indeed present in the environment and can contribute to the formation of soil through weathering, they themselves are not a direct component of soil. Instead, soil forms from the breakdown of these rocks into smaller particles, along with the addition of organic materials, water, and air. This distinction highlights that, while rocks are involved in the soil formation process, they are not components of soil itself as understood in soil science.