Final answer:
The two key features of the upper course of a river are erosion and deposition, as the river channel is steeper and water flows more rapidly here. option A is correct
Step-by-step explanation:
The two key features of the upper course of a river are erosion and deposition. In the upper course, where the river channel is steeper and narrower, the water flows more rapidly, leading to greater levels of erosion. This erosion picks up sediment and rocks, which the river can carry downstream.
Deposition in the upper course is generally less significant compared to erosion, but it can still occur, particularly when the river loses energy and drops some of the sediment it carries. option A is correct