What is the benefit of studying a river from source to mouth?

Correct answer: It helps understand erosion deposition uses and risks in different parts

The direct answer is A. A river is not the same everywhere. Near its source, the slope is usually steep and fast water mainly erodes the land. In the middle course, the river may transport sediment, form bends, and support settlements and farming. Near the mouth, the slope is gentle, deposition becomes important, and deltas or estuaries may occur. Studying the complete course therefore reveals different erosion, deposition, uses, and hazards. Option A is correct because it includes these changing physical and human features. Option B is wrong: studying the river does not change its name. Option C is wrong: different parts are not identical in slope, speed, landform, or work. Option D is wrong: studying a river cannot make its water disappear. A whole-system view helps explain floods, farming, transport, water supply, and conservation more accurately. Memory cue: source to mouth means changing slope, work, and risk.