The correct option is D Estuaries
In glacial regions close to the sea, due to the erosional action of the glacier, a huge depression forms and gets filled by seawater, forming a landform called a fjord. Fjords are partially submerged in the sea. Where the freshwater of the river meets the salty seawater or ocean water, a zone of brackish water is formed. This zone of transition where water is salty but not as salty as the ocean or sea is called an estuary.