You are presented with the question "Blowing what into a whistle causes sound?" and the following answer choices: 
- a lack of noise
 - CFCs
 - CO 2
 - a lack of sound
 - wind
 - air
 - gas
 - no noise

Now knowing that blowing air into a whistle causes air to vibrate inside the whistle and sounds are caused by vibrations in the air, choose the best answer.


 

      air   