Which role of rivers is important in forming alluvial plains?

Correct answer: Transport and deposition of sediments

The direct answer is option B, transport and deposition of sediments. Alluvial plains are broad, relatively level plains made mainly of alluvium, which means material such as sand, silt, clay, and small pebbles carried by rivers. A river erodes material upstream, transports it in its flowing water, and deposits it when its speed or carrying power decreases. Repeated deposition over long periods builds thick, fertile plains, especially near river valleys and floodplains. Option B is correct because both transport and deposition are necessary: the river must bring the sediment and then lay it down. Option A, only forming glaciers, is not the process that builds alluvial plains; glaciers are masses of moving ice. Option C, forming sea storms, is an atmospheric or oceanic process, not the main river process here. Option D, raising mountains, is related mainly to tectonic forces, not ordinary river deposition. A river can also erode and transport, but the landform in this question is specifically formed by deposited alluvium. Memory cue: alluvial means river-brought and river-deposited sediment.