The correct answer is: a) Contour farming
Contour farming is a type of agriculture that involves planting crops in rows that follow the natural contours of the land. This helps to reduce soil erosion and runoff, and it also helps to conserve water.
Mulching is a technique that involves covering the soil with a layer of organic material, such as straw or leaves. This helps to suppress weeds, retain moisture, and improve soil fertility.
Agroforestry is a system of agriculture that integrates trees and shrubs with crops and livestock. This helps to improve soil fertility, reduce erosion, and provide habitat for wildlife.
Monocropping is a system of agriculture in which a single crop is grown on a large area of land. This can lead to soil erosion, nutrient depletion, and the development of pests and diseases.
In conclusion, contour farming is the best agricultural technique for water conservation and weed control. It helps to reduce soil erosion and runoff, and it also helps to conserve water.