A fan-shaped deposit at the mouth of some rivers is called a (n)

a. pyramid

b. alluvial fan

c. dune

d. delta

A fan-shaped deposit (of sediment) at the mouth of some rivers is called b) an alluvial fan.

A dune is a mound of sand shaped by wind.

A delta is a sort of "tree" of splitting rivers at the mouth of a river.

B. Alluvial plan

is a fan shaped mass of alluvium deposited as the flow of a river decreases in velocity