Sound is produced by ______ which must travel through matter

:)

longitudinal waves :)

Sound is produced by waves of energy traveling through a medium (like air water rock metal etc but not a Vacuum), Specifically longitudinal waves, if you need to think of how you look like they are back and forth like stretching out a slinky and letting go of a few of the coils or like this.
(I II III IIIII IIIIII IIIII III II I II III IIIII IIIIII IIIII III II I) and so on going forward.

Longitudinal compression waves! The blank might be just waves though.

Hope this helps!

sound is produced by energy i guess