The repetition of sound caused by the reflection of sound waves is referred to as:

We will hear the same sound again if we shout or clap near a suitable reflecting object, such as a tall building or a mountain, a short time later. The sound we hear is referred to as an echo.

The phenomenon of sound wave reflection causes echoes to be heard.

For a person standing at the source to hear the echo clearly, the reflecting object must be more than 17.2 meters away from the sound source.

The phenomenon of sound reflection causes echoes to be heard. As a result, option 4 is correct.