In "Quantum Field Theory," the "Renormalization Group Flow" describes:
a) The change in the effective coupling constants of a theory as a function of the energy scale, providing insight into the behavior of quantum fields at different scales and the running of parameters like coupling constants.
b) The exact solutions of field equations in a static system.
c) The fixed points of a quantum field theory's parameters.
d) The interaction of particles in a low-energy regime.