In what type of environment do barchans mostly form?

Correct answer: Arid areas with limited sand and one dominant wind direction

Direct answer: Option C is correct. A barchan is a crescent-shaped sand dune formed where the supply of sand is limited and one prevailing wind direction is strong and fairly consistent. The wind pushes sand up the gentler windward slope and carries it over the crest; the two horns extend downwind. An arid setting is important because sparse vegetation allows sand to move freely. Option A is wrong because dense, humid forests hold sediment with vegetation and do not provide the usual open sandy surface. Option B is wrong because a deep marine trench is an underwater tectonic feature, not a wind-dune environment. Option D is wrong because permanent ice cover prevents mobile sand from accumulating in the required way. Option C includes both key conditions: limited sand and a dominant wind. Memory cue: “barchan = crescent dune + one main wind + little sand.”