What is the triangular depositional feature at a river mouth called?

Correct answer: Delta

A delta is a depositional landform that develops at a river mouth when the river enters a slower water body and loses carrying energy. Sand, silt, and clay settle there, often producing a roughly triangular plain crossed by distributary channels. Hence option A is correct. A cirque is glacial, a yardang is wind-eroded, and a sea cave is carved by waves along a coast.