- A person speaking is a source of sound
- Echo is when sound reflects off of a surface
- So, the sound of a person speaking can reflect off of a surface and produce echo

- The sound of a person speaking can reflect off of a surface and produce echo
- Cave walls are a kind of surface
- Hence, if a person makes sound in the cave, then the sound will reflect off from the cave wall and produce echo

Therefore, if a person makes sound in the cave, then the sound will reflect off from the cave wall and produce echo
Question
Some students were on a tour exploring the inside of a cave. While the students were in the cave, they realized they heard an echo every time that they spoke. Which most likely caused the echo to occur?

Context
- A person speaking is a source of sound 
- Echo is when sound reflects off of a surface 
- Cave walls are a kind of surface