Answer is: D) sound.
Sonar (SOund Navigation And Ranging) is a technique that uses sound propagation to navigate.
The acoustic frequencies used in sonar systems vary from very low (infrasonic) to extremely high (ultrasonic).
Sound waves travel faster in more dense material, and the more dense the material the louder the sound is.
The velocity of sound in seawater changes with water pressure, depth, temperature and salinity.
Sound energy - this type of energy travels through vibrations on waves.
