Which process is main in delta formation?

Correct answer: Deposition of sediment by a river

The direct answer is A, deposition of sediment by a river. A river carries sand, silt, clay and small stones from higher land. Near its mouth, where the river enters a sea or lake, the river usually slows down. A slower current cannot carry as much material, so the sediment settles and accumulates. Over time, this deposited material may build a delta, often with distributary channels. Option B describes glacier formation in mountains, not delta formation. Option C is unnecessary and incorrect because a sea does not have to dry up for a delta to form. Option D describes a desert landform made mainly by wind, not a river delta. Thus deposition at the river mouth makes A correct. The exact shape and size of a delta also depend on waves, tides and currents, but deposition is the key process in this school-level question. Memory cue: river slows, load settles, delta develops.