ANS:D - all of these.

The ratio of design discharge to the surface area of a sedimentation tank is commonly referred to as surface loading. This parameter helps in determining the capacity and efficiency of the sedimentation tank in removing suspended solids from the water. So, the correct term is "surface loading." The other terms mentioned - overflow rate and overflow velocity - are related to different aspects of sedimentation tank performance. Overflow rate typically refers to the rate at which water overflows from the tank, usually expressed in gallons per minute per square foot or similar units. Overflow velocity refers to the velocity of the water as it exits the sedimentation tank overflow weir. While these terms are important in understanding the hydraulic performance of sedimentation tanks, they are not specifically related to the ratio of design discharge to surface area.