The correct answer is C. drooping voltage characteristics.
Shunt generators are most suited for stable parallel operation because of their drooping voltage characteristics. This means that as the load on the generator increases, the voltage of the generator decreases. This helps to maintain a constant voltage in the system, even as the load changes.
Option A is incorrect because rising voltage characteristics would make it difficult to maintain a constant voltage in the system. Option B is incorrect because identical voltage characteristics would mean that the generators would not be able to share the load evenly. Option D is incorrect because linear voltage characteristics would not provide enough stability to the system.
Here is a diagram that illustrates the drooping voltage characteristics of a shunt generator:
[Diagram of a shunt generator with a drooping voltage characteristic]
As the load on the generator increases, the current through the field winding decreases. This causes the magnetic field to weaken, which in turn causes the voltage of the generator to decrease. The amount of droop is determined by the design of the generator.
Drooping voltage characteristics are important for stable parallel operation because they help to ensure that all of the generators in the system share the load evenly. If one generator had a rising voltage characteristic, it would take on more of the load than the other generators, which could lead to instability in the system.
I hope this explanation is helpful!