ANS:C - 1 in 100 downward

"1 in 100 downward" refers to a gradient where for every 100 units of horizontal distance, the vertical elevation decreases by 1 unit. This indicates a downward slope or descent. In the context of sewer lines or drainage systems, a downward gradient is often desirable to ensure proper flow of wastewater or stormwater towards the treatment facilities or outfall points. A downward gradient helps in facilitating the movement of fluids through gravity, which can reduce the need for additional pumping or energy-intensive methods to convey wastewater. So, "1 in 100 downward" means that for every 100 meters of horizontal distance, the sewer line drops by 1 meter vertically. This gradient ensures efficient drainage of wastewater along the sewer line.