Because they are non renewable sources of energy and they took billions of years to form.
The Paleozoic Era ended with the largest extinction event in the history of Earth, the Permian–Triassic extinction event. The effects of this catastrophe were so devastating that it took life on land 30 million years into the Mesozoic Era to recover
I would go for C. Accuracy is the best one if you have the right information then your numbers should be right