* Sound waves are mechanical waves: This means they require a medium (matter) to travel through. They are vibrations that transfer energy through the medium.

* Solids, liquids, and gases are elastic materials: This means they can deform under stress and return to their original shape when the stress is removed. This ability to deform and restore is essential for sound waves to propagate.

* A vacuum has no matter: Therefore, sound waves cannot travel through a vacuum.

Let's break down why the other options are incorrect:

* A solid: While sound travels well through solids (think of how clearly you hear a knock on a wooden door), it's not the only medium.

* B liquid: Sound travels through liquids as well. You can hear sounds underwater.

* D vacuum: As mentioned, a vacuum is completely empty of matter, so sound waves cannot travel through it.

Let me know if you'd like more detail on how sound waves travel through different mediums!