In the diagram, above, marker d is pointing to a which is a landform that forms when a river slows down as it flows into an ocean or lake. as the river slows, it drops its sediment load, gradually creating a network of small channels and islands.

The correct answer is delta.

In the diagram, above, marker D is pointing to a delta, which is a landform that forms when a river slows down as it flows into an ocean or lake. As the river slows, it drops its sediment load, gradually creating a network of small channels and islands.
There exists the same question from other source that has the image or the diagram showing a map.

Bwould be my guess |-/