The picture illustrates a waterfall which is a common landform in the youthful stage of a river. In this stage, vertical erosion (C) dominates as a result of the steep gradient which promotes abrasion (i.e. the wearing away of bedrock caused by the rubbing, scouring, or scraping action of rock fragments or particles carried by streams, ice, wind, or waves.).

Lateral erosion (B) occurs in the mature and old stages of a river as the gradient decreases. Deflation (A) is a lowering of the land due to wind erosion. Option (D) is a definite distracter.