At the junction of sewers A. Top of smaller sewer is kept lower B. Top of larger sewer is kept lower C. Tops of both the sewers are at the same level D. None of these

The correct answer is: C. Tops of both the sewers are at the same level.

The purpose of a sewer junction is to allow two or more sewers to connect and flow into each other. The tops of the sewers must be at the same level in order for this to happen. If the tops of the sewers were not at the same level, the sewage would not be able to flow properly and could back up.

Option A is incorrect because the top of the smaller sewer would be lower than the top of the larger sewer. This would create a blockage and prevent the sewage from flowing.

Option B is incorrect because the top of the larger sewer would be lower than the top of the smaller sewer. This would also create a blockage and prevent the sewage from flowing.

Option D is incorrect because the tops of both the sewers must be at the same level in order for the sewer junction to work properly.