We know in suitable condition every sound echoes.But there is one sound which does not echo.Guess the sound ?

Keep practicing — related questions

• Whose noise doesn’t have echo and no one researched why?
• Whose noise doesn’t have echo and no one researched why?
• A duck's quack doesn't echo, and no one knows why.
• A duck's quack doesn't echo, and no one knows why.
• Why doesn't a duck's quack echo?
• A duck's quack has an echo.
• A duck's quack doesn't echo.
• A duck's quack has echo.