Explain the conditions in which a person can or can't hear a echo

When your in the mountains or in a quiet room

Explained

Explanation:

The necessary condition for an echo to occur are

1) The distance between the sound source and the object of reflection must be equal to or greater than 17 meters.

2) the time period between hearing the original sound and the echo must not be less than 0.1 second, because human ear is not that sensitive to distinguish between two sounds within a gap of time less than 0.1 second.