- A canyon wall is a kind of surface
- Echo is when sound reflects off of a surface
- Therefore, sound can reflect off the canyon wall and produce an echo

So, sound can reflect off the canyon wall and produce an echo
Question: Campers shouted toward a canyon wall. What characteristic of sound best explains why the campers heard an echo?
Context: - A canyon wall is a kind of surface 
- Echo is when sound reflects off of a surface