C. They are energy being transferred through matter or space.
Explanation:
Waves which are ripple effect gotten when a matter is subjugated to vibration is common among the various medium such as water or spring. This ripple effect happens to be energy which moves from region where it is generated and spread outwards towards regions where is not felt.
<em>Example is a stone dropped in the middle of the water. It (water wave) spreads from the middle towards the outer part of the container which houses the water.</em>
