Barchan dunes of Thar are not considered river landforms because they are formed by what?

Correct answer: Transport and deposition of sand by wind

The direct answer is A: barchan dunes form through transport and deposition of sand by wind. A barchan is a crescent-shaped sand dune found mainly in dry deserts where wind blows mostly in one prevailing direction and sand is limited. Reasoning: there is loose sand; wind lifts or pushes it; the wind carries it; when its speed or carrying ability decreases, sand is deposited; repeated deposition builds a dune. Option A is correct because this is an aeolian, or wind-made, landform. Option B is wrong because river silt makes fluvial deposits, not desert dunes. Option C is wrong because glacial ice creates glacial landforms. Option D is wrong because coral rock forms in marine environments, not from moving desert sand. Exam cue: dunes indicate wind action; river landforms indicate running water.