ANS:E - all the above.

In an inclined pipe, the pressure difference at its two ends is primarily due to:

1. Elevation Head: The pressure difference in the pipe due to the difference in elevation between the two ends contributes to the overall pressure gradient along the pipe. The elevation head is a component of the total energy of the fluid in the pipe.
2. Frictional Loss Head: As the fluid flows through the pipe, it experiences frictional resistance against the walls of the pipe. This frictional resistance results in a loss of energy, known as frictional loss head. This loss of energy contributes to the pressure difference between the two ends of the pipe.
3. Sudden Head Drop at Inlet or Exit Head Drop: If there are sudden changes in the cross-sectional area of the pipe at the inlet or outlet, such as abrupt expansions or contractions, they can lead to sudden changes in flow velocity and pressure. These changes can cause head drops at the inlet or exit, which also contribute to the overall pressure difference along the pipe.

Therefore, the pressure difference at the two ends of an inclined pipe is influenced by various factors, including elevation head, frictional loss head, and any sudden changes in flow conditions at the inlet or outlet. Thus, the correct answer is "all the above."