Concept:Polarization happens only for transverse waves.Explanation:A transverse wave vibrates at right angles to the direction it travels, so its vibrations can be restricted to one plane.A longitudinal wave vibrates along the direction of travel, so it cannot be polarized.Diffraction, reflection, and refraction affect both transverse and longitudinal waves.Therefore, polarization is the unique property used to identify a transverse wave.Answer:D. polarization