Which combination is most favourable for delta formation at a river mouth?

Correct answer: Low velocity high sediment and shallow calm coastal area

Direct answer: A, low velocity, abundant sediment, and a shallow calm coastal area. A delta forms where a river enters a standing water body and loses speed. The reasoning is: the river carries sediment; near the mouth its velocity falls; it can no longer carry all the load; sediment is deposited in layers; repeated deposition builds a delta. A provides every favourable condition. B is wrong because a steep mountain slope usually keeps water fast and sediment-free water cannot build a deposit. C describes a desert basin, not the normal river-mouth setting. D reverses the direction of a river, because rivers flow toward the sea rather than begin from it. Exam cue: delta means deposition at a river mouth, especially where currents and waves do not remove the sediment.