The correct answer is C. Pulse broadening at output.
Intermodal dispersion is a type of pulse broadening that occurs in multimode step index fibers. It is caused by the different paths that light takes through the fiber, which results in different arrival times at the output. This can cause significant pulse broadening, which can limit the transmission speed of the fiber.
Attenuation is a decrease in the power of a signal as it travels through a medium. It is caused by absorption and scattering of the signal. Attenuation is a major factor in limiting the transmission distance of optical fibers.
Propagation is the movement of a wave through a medium. In the case of optical fibers, the wave is light. Propagation is affected by the refractive index of the fiber, which is the ratio of the speed of light in a vacuum to the speed of light in the fiber.
The other options are incorrect because they do not describe the effect of intermodal dispersion.