Final answer:
The propagation speed in mechanical waves is established by changing the ratio of displacement over the change of the ratio of wavelength.
Step-by-step explanation:
The propagation speed in the study of mechanical waves is established by changing the ratio of the displacement over the change of the ratio of the wavelength.
For example, if we have a wave with a larger displacement and the same wavelength as another wave, the wave with the larger displacement will have a higher propagation speed.
Therefore, the correct answer is A) displacement; wavelength.