Wanda and Marita are drinking bottles of water. Each girl sounds a different musical note by blowing across the top of her bottle. What is a good hypothesis that could lead to new experimentation?

It is more fun to play musical notes with carbonated water than with normal spring water.
If the lid on a bottle is tightly closed, then blowing across the top of the bottle will not make a musical note.
Blowing across the top of a bottle can make a musical note.
If there is less water in the bottle, then the note played is lower because there is more air to move around.