Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Bruce plays his violin every Friday night for the symphony. Before he plays, he plucks each string to see if his violin is in tune. Which is most responsible for the generation of sound waves from his violin?
Vibrating strings.