The answer is the second one: Many Mongolians are pastoral nomads who raise livestock for a living.
Im sire the answer for this is letter C “territory”
Flood Erosion and Deposition: As flood waters rise, the slope of the stream as it flows to its base level (e.g., the ocean or a lake) increases. ... Both of these factors lead to an increase in stream velocity. The increased velocity and the increased cross-sectional area mean that discharge increases.
Hope the resolution is good enough to read. Hope this helps :)