An echo is caused by:

**The reasoning** An echo happens when sound waves **bounce back** to you after hitting a hard surface like a wall, mountain, or building. This bouncing-back process is called **reflection**. Think of it like throwing a ball against a wall — it comes back to you, right? Sound does the same thing. When you shout in an empty hall or near a cliff, the sound travels away, hits the surface, and reflects back to your ears as an echo. That's why you hear your voice again after a short delay. **Why the wrong options tempt you** - **Refraction** is sound bending when moving between different materials (like air to water) — it doesn't create echoes. - **Diffraction** is sound spreading around obstacles — think of hearing someone around a corner, not hearing yourself twice. - **Interference** is when two sound waves meet and combine — that's not about sound bouncing back. **Quick takeaway** Echo = sound **reflecting** (bouncing back) from a surface, just like light in a mirror or a ball off a wall.