Option B: cooling as the lava runs down the mountain
Explanation:
The point R is basically at near the Earth's surface.
Now, we are told that rocks melt underground to form magma. This is a process of formation of igneous rocks. So, in formation of igneous rocks another process that will contribute to formation of rocks at point R is named cooling.
Cooling is a process where the larva runs down the mountain that makes magma hardened and makes it it turn into igneous rock.
