The correct answer is C. Soliton propagation.
A soliton is a self-reinforcing wavepacket that maintains its shape while propagating in a nonlinear dispersive medium. Solitons are formed when the nonlinear chirp caused by self-phase modulation balances, postpones, the temporal broadening induced by group velocity delay.
Four wave mixing is a nonlinear optical phenomenon in which three waves interact to produce a fourth wave. Phase modulation is a process in which the phase of a wave is changed by an external influence. Raman scattering is a scattering process in which light interacts with matter and is scattered inelastically, with the energy of the scattered light being changed.
In conclusion, soliton propagation is the result of a case of nonlinear dispersion compensation in which the nonlinear chirp caused by self-phase modulation balances, postpones, the temporal broadening induced by group velocity delay.