If you walk into an empty gym and yell,why would you hear an echo? The gym walls are soft and uneven. The sound waves are being absorbed by the hard smooth walls. The sound waves are bouncing off the hard smooth gym walls. The sound waves are being cancelled due to destructive interference.

## Step 1<br />An echo is a sound that is reflected off a surface and heard again. This phenomenon occurs when the sound waves bounce off a hard, smooth surface, such as the walls of a gym. <br /><br />## Step 2<br />The gym walls are hard and smooth, which means they do not absorb the sound waves. Instead, they reflect them. This is why you can hear an echo in an empty gym.<br /><br />## Step 3<br />The other options are incorrect because they do not accurately describe the conditions necessary for an echo to occur. The gym walls are not soft and uneven, nor are the sound waves being absorbed by the hard smooth walls. Also, the sound waves are not being cancelled due to destructive interference.