B), (C) and (D) are correct.Soil erosion:It is the natural process in which the topsoil i.e fertile soil is carried away by physical sources LIKE wind and water.It is a continuous process which occurs either slowly or at an ALARMING rate.Causes:Rainfall and FloodingAgricultureOver GrazingLogging and Mining Rivers and StreamsHeavy WindsConservation Methods:AfforestationContour PLOUGHING (cultivation against the direction of the wind)Flood ManagementReclamation of badlandsOrganic farmingConstruction of proper drainageLevelling of gullies, ravines etcProper awareness about the need for conservation.