The correct answer is: d) All of the above.
Afforestation is the process of planting trees on land that was previously not forested. This can help to prevent soil erosion by providing a barrier between the soil and the wind and rain. It can also help to improve the water quality by filtering out pollutants.
Contour farming is a method of farming that involves planting crops in rows that follow the contours of the land. This helps to prevent soil erosion by reducing the amount of runoff water. It can also help to improve the water retention of the soil.
Crop rotation is a method of farming that involves planting different crops in the same field each year. This helps to prevent soil depletion by allowing different crops to take up different nutrients from the soil. It can also help to reduce the risk of pests and diseases.
All of these methods can help to promote soil conservation in Bihar.