which are examples of a medium?\nwater and air\namplitude and wavelength\ncrests and troughs\ncompressions…

Brief Explanations:

A medium is a substance through which a wave can travel. Water and air are substances that can allow waves (like sound or water - waves) to propagate. Amplitude and wavelength are properties of waves, crests and troughs are parts of a transverse wave, and compressions and rarefactions are parts of a longitudinal wave.

Answer:

water and air