The correct answer is: D. both (A) and (B)
The coefficient of discharge of an ogee spillway is a dimensionless number that is used to calculate the discharge of water over the spillway. It is a function of the depth of approach, upstream slope, downstream apron interference, and downstream submergence.
The depth of approach is the depth of water upstream of the spillway. The upstream slope is the slope of the channel upstream of the spillway. The downstream apron interference is the effect of the downstream apron on the flow of water over the spillway. The downstream submergence is the depth of water downstream of the spillway.
The coefficient of discharge is a complex function of these four variables. It is typically determined experimentally.
The coefficient of discharge is important because it is used to calculate the discharge of water over the spillway. The discharge of water over the spillway is important for flood control and for the operation of hydroelectric power plants.