Concept:Loess is a fine, wind-deposited sediment.Explanation:Wind erosion and transport can carry very fine particles like sand and silt over long distances.When the wind slows down, these particles settle and accumulate as a loose, layered deposit.This deposit is called loess.It is often found in regions like North-West China.In the options, loess is the correct term for a layer of very fine wind-deposited sand and silt.Answer:A. loess