The correct answer is: A. Near the inner surface of the pipe.
Large diameter sewers subjected to external pressure alone, are reinforced near the inner surface of the pipe. This is because the pressure from the soil outside the pipe acts on the outer surface of the pipe, and the reinforcement helps to resist this pressure. The reinforcement is typically made of steel or concrete, and it is placed in a helical or spiral pattern around the circumference of the pipe.
The other options are incorrect. Option B is incorrect because the reinforcement is not placed near the outer surface of the pipe. Option C is incorrect because the reinforcement is not placed both near the inner and outer surfaces of the pipe. Option D is incorrect because the reinforcement is not made with an elliptical cage.