The correct answer is A. Rayleigh scattering.
Rayleigh scattering is a form of scattering that is caused by the interaction of electromagnetic radiation with particles of a much smaller wavelength. In the context of fiber optics, Rayleigh scattering is caused by the interaction of light with the imperfections in the fiber, such as core-cladding RI differences, diameter fluctuations, strains, and bubbles.
Mie scattering is a form of scattering that is caused by the interaction of electromagnetic radiation with particles of a similar wavelength. In the context of fiber optics, Mie scattering is caused by the interaction of light with the impurities in the fiber, such as dust and water droplets.
Stimulated Brillouin scattering is a form of scattering that is caused by the interaction of light with the acoustic waves in the fiber. In the context of fiber optics, stimulated Brillouin scattering is used to generate optical frequency combs.
Stimulated Raman scattering is a form of scattering that is caused by the interaction of light with the vibrational modes of the molecules in the fiber. In the context of fiber optics, stimulated Raman scattering is used to amplify light signals.