How does the direction of erosion generally change in the middle course of a river?

Correct answer: Vertical erosion decreases and lateral erosion increases

Correct answer: A. A river’s course is commonly understood as upper, middle, and lower sections, although the exact changes are gradual rather than sudden. In the upper course, the land is usually steeper, so downward or vertical erosion is prominent and the valley may become deep and narrow. In the middle course, the slope generally becomes gentler and the river carries more water. The river then uses more of its energy to erode the sides of its channel, called lateral erosion. This widens the valley and can encourage meanders. Option A is correct. Option B is wrong because erosion does not stop completely. Option C is wrong because glacial erosion is done by moving ice, not newly beginning river action. Option D is wrong because sea waves are not the normal work of a river channel. Memory cue: upper course cuts down; middle course cuts sideways.