The correct answer is C. Erosion.
Erosion is the process by which soil is moved from one place to another by the action of wind, water, or ice. It is a natural process that has been occurring for millions of years. However, human activities, such as deforestation and agriculture, have accelerated the rate of erosion.
Radiation is the emission of energy in the form of waves or particles. It can be natural, such as from the sun, or man-made, such as from nuclear power plants. Radiation does not cause soil to form.
Weathering is the process by which rocks are broken down into smaller pieces. It is caused by physical forces, such as wind and water, and chemical reactions. Weathering is a necessary process for the formation of soil.
Pollution is the contamination of the environment with harmful substances. It can be caused by human activities, such as industrial emissions, or natural events, such as volcanic eruptions. Pollution does not cause soil to form.
In conclusion, the correct answer is C. Erosion.