Answer:
The upper course, middle course, and lower course are the three parts of the river.
Step-by-step explanation:
The source of a river can be found on the upper course. The land is usually high and mountainous, and the river has a steep gradient with fast-flowing water. There is a lot of weathering and erosion. The rivers are divided into three parts: the upper part, the central part, and the lower part. The upper part is closer to the source of a river. The earth is generally high and mountainous, and the river has a steep gradient with water flowing rapidly. There is a lot of vertical erosion and inflexible weather.