The correct answer is B) The viscosity of the fluid is relatively unimportant in the pump operation. Spur gear pumps are designed to handle a wide range of fluid viscosities, from light oils to heavy, viscous fluids. The shape and design of the gear teeth allow the pump to effectively move and displace the fluid regardless of its viscosity. Unlike some other pump types, the viscosity of the fluid being pumped does not significantly affect the operation of a spur gear pump. The other answer choices are incorrect because: A) Spur gear pumps can handle a wide range of fluid viscosities, not just light oils. C) There is no viscosity limit on the fluids that a spur gear pump can handle. D) Spur gear pumps are not limited to only high viscosity fluids.