the accumulation of the sound waves the diffraction of the sound waves the refraction of the sound waves the reflection of the sound waves
I am hesitating between 4 options to answer the following question, which option should I choose?
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?
Possibilities:
- the accumulation of the sound waves
- the diffraction of the sound waves
- the refraction of the sound waves
- the reflection of the sound waves

the reflection of the sound waves