Why do river deltas on the Eastern Coastal Plain extend the plain seaward?

Correct answer: Because rivers deposit transported alluvial material at their mouths

Direct answer: B, because rivers deposit transported alluvial material at their mouths. A delta forms where a river enters a slower body of water such as a sea or lake and loses carrying energy. Step by step: the river erodes and carries sediment upstream; near the mouth, flow slows; sand, silt, and clay settle; repeated deposition builds channels and a triangular or fan-shaped landform outward. This adds land to the coastal plain seaward. Option A is wrong because the sea is present at the river mouth. Option B is correct and gives the actual process. Option C, submerged Eastern Ghats, is not the general cause of delta growth. Option D, coral organisms building mountains at every mouth, is scientifically wrong; deltas are mainly river sediments, not coral mountains. Memory cue: river carries, mouth slows, sediment settles, delta grows.