Ventilating shafts are provided to a sewer line at every

ANS:D - 300 m

Ventilating shafts are provided to a sewer line at intervals typically ranging from 150 meters to 300 meters. These shafts serve to provide ventilation to the sewer system, allowing foul gases to escape and fresh air to enter. The spacing between ventilating shafts depends on factors such as the length of the sewer line, topographical conditions, and the need to ensure adequate airflow and ventilation throughout the system. Therefore, the correct option is: Between 150 meters to 300 meters.