ANS:B - seas

Sludge banks can form when sewage is disposed of in rivers, seas, or lakes. When sewage containing organic matter and other pollutants is discharged into water bodies, it can lead to the accumulation of sludge along the banks or at the bottom of the water body. This sludge consists of sediment and organic matter that settle out from the sewage over time. It can pose environmental hazards and negatively impact aquatic ecosystems and water quality. Therefore, proper sewage treatment and disposal methods are essential to prevent the formation of sludge banks and minimize environmental pollution.