Based on the information provided, larger holes in drilled rocks are generally associated with petroleum drilling, as this method often involves larger diameter drills to access oil reservoirs. Smaller holes are typically associated with copper drilling, which often occurs through narrower or deeper drilling methods.
Given those tendencies, the most reasonable conclusion would be:
"The rock display with larger holes shows petroleum drilling, which is deeper underground."
It's important to understand that drilling for petroleum can occur at various depths, but the larger holes are typically indicative of methods used to drill for petroleum resources. On the other hand, copper drilling is often more precise and may require smaller holes. If we had to choose one from your options based on common drilling knowledge, we'd go with the first part of that reasoning. However, the specifics of the depth can vary depending on many factors like location and geology.