Concept:Soil erosion control should match the slope and climate; contour ridging is best for gentle slopes in humid regions.Explanation:Contour ridging involves making ridges along the slope contour, which slows down running water and reduces erosion.It is suitable for gentle slopes and humid areas where rainfall is heavy.Terrace cultivation is better for steeper slopes.Intercropping helps cover the soil but is not the best direct erosion-control technique for gentle slopes.Wind breakers are used mainly to control wind erosion in dry areas.Answer:A. contour ridging