Solution:A river begins at source (or more often several sources) follows a path course and ends at a mouth or mouths. River landforms can be divided into upper, middle and lower course features.
Upper course features include steep-sided V shaped valleys, interlocking spurs, rapids, gorges and waterfalls.
Waterfalls or simply falls are caused because of sudden descents or abrupt breaks in the longitudinal course of the river due to a hist of factors like variation in the relative difference in topographic reliefs, fall in the sea levels, Earth movements etc.
It may be defined as a vertical drop of water of enormous volume from a great height. Middle course river features include wider, shallower valleys, meanders and Oxbow lakes. Meanders refer to the bends of longitudinal courses of the river.
Each bend of a meander has two types of slopes of valley side. One side in concave slope and the other side is convex slope. The neck of the meander gets narrower and narrower. Eventually, the curve grows so tight that the river cuts through the meanders neck.
This separated area of water is called an oxbow lake. Delta formation occurs at the lower course of river. A river delta is a landform created by deposition of sediment that in carried by the river as the flow leaves its mouth and enters slower moving or stagnant water. Hence, option (b) is correct.