Please send help also 20points

An echo occurs when a hits something hard?

im thinking its a soundwave but im not sure

ill mark brainliest if its the right answer

sound wave

Explanation: Echo is a sound heard after a sound wave hit a hard surface. The sound is what is heard back as echo. An echo doesn't occur when the sound wave have been absorbed before hitting an hard surface so in a large crowd you might not hear an echo because the sound wave have been absorbed. The echo is heard faster when you are standing close to a hard surface than when you are far away a hard surface.

one centimetre is equal to 0.01 metres