Fact 1: Blowing air into a whistle causes air to vibrate inside the whistle.

Fact 2: All sounds begin with vibrations.

Given the two facts above, answer the question "what do whistles use to make sound?" with the following options: 
- Collagen
 - air
 - Energy.
 - power
 - oxygen
 - waves
 - friction
 - energy


 

     oxygen    