ANS:D - none of these.

Frictional loss of head includes the loss of energy due to both viscosity and turbulence. Frictional loss of head, also known as head loss due to friction, occurs when a fluid flows through a conduit or pipe. It includes the loss of energy caused by the interaction between the fluid and the surface of the conduit or pipe, which results in frictional resistance to flow. Viscosity plays a significant role in frictional loss because it creates internal resistance within the fluid as it flows through the pipe. Turbulence also contributes to frictional loss by causing additional mixing and swirling of the fluid, which dissipates energy. Therefore, the correct statement is: Frictional loss of head includes the loss of energy due to both viscosity and turbulence.