Final answer:
The correct answer is 'B) Volcanic eruption / Igneous rock' because Stone Mountain was formed from solidified magma, making it an igneous rock.
Step-by-step explanation:
Stone Mountain was formed as a result of the upwelling of magma from within the Earth's crust during the formation of the Blue Ridge Mountains about 300-350 million years ago, which is part of the Appalachian Mountains. This upwelling of magma solidified to form igneous rock that became Stone Mountain. Therefore, the correct answer to the question is 'B) Volcanic eruption / Igneous rock'.