vibrations on the ground vibrations of the air seismic waves light waves
I gave my students this multiple choice question: During a sporting event, a referee uses a whistle to alert the teams to start and stop playing. What causes the sound from the referee's whistle to travel in all directions?

Only one answer is correct among these 4 choices:
- vibrations on the ground
- vibrations of the air
- seismic waves
- light waves

Could you tell me which one is correct?

vibrations of the air