Question

which are examples of a medium?
water and air
amplitude and wavelength
crests and troughs
compressions and rarefactions

Explanation:

A medium is a substance through which a wave can travel. Water and air are substances that can carry waves (e.g., water waves, sound waves in air). Amplitude and wavelength are wave properties. Crests and troughs are parts of a transverse wave. Compressions and rarefactions are parts of a longitudinal wave.

Answer:

water and air