The correct answer is: D. waterfalls
A waterfall is a place where water flows over a vertical drop or a series of steep drops in the course of a stream or river. Waterfalls form when the water flow in a river is too strong to erode the riverbed evenly. The water erodes the riverbed more quickly at the bottom of the drop, creating a vertical drop. The water then flows over the edge of the drop and continues down the river.
Landslides are a type of mass wasting that occurs when a large mass of rock, soil, or debris moves down a slope. Landslides can be caused by a variety of factors, including earthquakes, heavy rains, and human activities.
Canyons are deep, narrow valleys with steep sides. Canyons are formed by the erosion of rivers and streams over time. The water in the river or stream erodes the land, creating a deep valley. The sides of the valley are steep because the water erodes the land more quickly at the bottom of the valley.
Gorges are similar to canyons, but they are even deeper and narrower. Gorges are formed by the same process as canyons, but they are more extreme. The water in the river or stream erodes the land even more quickly, creating a very deep and narrow valley.
In conclusion, the formation of waterfalls is the most characteristic feature in upper course of a river. This is because waterfalls form when the water flow in a river is too strong to erode the riverbed evenly. The water erodes the riverbed more quickly at the bottom of the drop, creating a vertical drop. The water then flows over the edge of the drop and continues down the river.