ANS:C - fluid temperature.

The magnitude of water hammer caused in pipe flow is independent of the fluid temperature. Water hammer occurs when there is a sudden change in fluid velocity or direction within a pipe system, typically caused by the rapid closure of a valve or the sudden start or stop of a pump. This abrupt change in fluid momentum generates pressure waves that propagate along the pipe, resulting in a sudden increase in pressure known as water hammer. The magnitude of water hammer depends on various factors, including the fluid velocity, the rate of fluid flow stoppage, the length and diameter of the pipe, and the elasticity of the pipe material. However, the fluid temperature does not significantly affect the magnitude of water hammer. Instead, it primarily influences the fluid properties such as viscosity and density, which can affect the damping characteristics of the system but do not directly impact the magnitude of water hammer. Therefore, among the options provided, the magnitude of water hammer is independent of the fluid temperature.