caused by physical vibrations. moved by the force of gravity. types of electromagnetic waves. of the same frequency.
I gave my students this multiple choice question: The waves that are produced by a person's voice are similar to the waves produced by an earthquake because both are

Only one answer is correct among these 4 choices:
- caused by physical vibrations.
- moved by the force of gravity.
- types of electromagnetic waves.
- of the same frequency.

Could you tell me which one is correct?

caused by physical vibrations.