Answer:
<h2>C. Core Sample</h2>
Explanation:
A core sample is a cylindrical section of (usually) a naturally-occurring substance. Most core samples are obtained by drilling with special drills into the substance, such as sediment or rock, with a hollow steel tube, called a core drill. The hole made for the core sample is called the "core hole".
The answer is decay. Decay is the principal natural means of recycling solid waste.