The air expands. The fork releases electrons. The particles in the objects vibrate. The water in the glass forms ripples.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Why does tapping a fork against a water glass produce a sound?
Possibilities:
- The air expands.
- The fork releases electrons.
- The particles in the objects vibrate.
- The water in the glass forms ripples.

The particles in the objects vibrate.