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

Fact 2: Sounds are vibrations in air.

Given the two facts above, answer the question "What does blowing into a whistle cause?" with the following options: 
- wind
 - energy
 - waves
 - sound
 - Injury
 - ice
 - Energy.
 - heat


 

    sound     