Question

what is the reduction of topsoil by water and wind?
soil sapping
soil erosion
soil stripping
soil conservation

Explanation:

Soil erosion is the process where the topsoil is removed by natural agents like water and wind. Soil sapping is related to water flow in soil pores. Soil stripping is more about human - induced removal (like mining). Soil conservation is about protecting soil.

Answer:

soil erosion