ANS:D - all the above.

The gradient of sewers depends upon all the above factors:

1. Velocity of flow: The gradient of a sewer is determined in part by the desired velocity of flow. A sufficient gradient is required to achieve the desired velocity of flow to transport sewage effectively without causing sedimentation or blockages.
2. Diameter of the sewer: The diameter of the sewer influences the gradient required for proper flow. Larger diameter sewers generally require less gradient to maintain adequate flow velocities compared to smaller diameter sewers.
3. Discharge: The discharge, or the amount of sewage flow, also influences the gradient of sewers. Higher discharge rates typically require steeper gradients to maintain adequate flow velocities and prevent sedimentation or blockages.

In summary, the gradient of sewers is influenced by the velocity of flow, diameter of the sewer, and discharge. Each of these factors plays a role in determining the appropriate gradient required for efficient sewage transport and drainage within the sewer system.