To complete the statement based on the provided options, the correct response is likely to be wavelength if the bottom wave is visually longer compared to the top wave, or amplitude if it is taller. If you're referring to the physical distance between two consecutive peaks, then the response would be wavelength. If you're talking about the height of the wave from the baseline to the peak (or the depth of the trough), then it would be amplitude.
Without seeing the diagram, if we assume the bottom wave looks longer, you should choose wavelength. If it appears taller, choose amplitude.
Please specify what aspect you’re looking at to finalize the answer.