Answer:3-Sonar
Explanation:
Sonar system is used to detect the under water objects by using the deflection of sound waves.
Sonar is an acronym of Sound navigation ranging.Two types of sonar sets are used for working: active and passive. The active sonar system pushes out sound signals called pings, and then absorbs the return sound echo. Passive sound sets obtain sound echoes without transmitting their actual sound signals. Submarines are using sonar to track other vessels.
