The speed of a river is high near the watershed such up the mountains. Therefore the rate of erosion in his region is high. The sediments are carried and as the river speed decreases in the lower elevation areas such as the coastal areas, it begins to deposit the sediments. This is how deltas are formed. This is also why the river beds up in higher elevation is more V=shaped and in lower elevation is U-shaped.
The answer is; B
Contour plowing is done in the highly mountainous or hilly area. It reduces erosion in agriculture in these areas because the steepness increases erosion of bare soil without vegetation. Since farming exposes the soil, contour plowing reduces the rate of soil erosion by leveling soild across the slope following its elevation contour lines.
