Blowing air into a whistle causes air to vibrate inside the whistle.
Sounds are caused by vibrations in the air.
Blowing air into a whistle causes sound.
Blowing what into a whistle causes sound?
Options:
[1] a lack of noise
[2] CFCs
[3] CO 2
[4] a lack of sound
[5] wind
[6] air
[7] gas
[8] no noise