ANS:D - toilets.

The sludge typically does not contain wastewater from wash basins, kitchen sinks, or bath rooms. Sludge primarily consists of solid materials that settle out during the wastewater treatment process. These solids include organic matter, suspended particles, and microbial biomass. Wastewater from wash basins, kitchen sinks, and bath rooms usually contains dissolved and suspended organic matter, grease, soap residues, and other contaminants that remain in the liquid phase and are treated separately in the wastewater treatment process. However, wastewater from toilets, which includes human waste and flush water, contributes to the formation of sludge as it contains solid human waste, toilet paper, and other materials that settle out during treatment. Therefore, the correct answer is: d. toilets.