Answer :
The answer is "C", and then you have two different types of igneous rocks, one being extrusive (magma that cools faster, and cools on/near the surface, results in obsidian, basic rock, etc), and intrusive (magma that cools slowly and is inside the earth, forms diamonds and other gems of high value and appearance).
Answer:
The most appropriate answer would be C. melting and cooling.
Igneous or magmatic rock is mainly formed by cooling and solidification of lava or magma.
Melting can be done by either one or more processes such as a decrease in pressure, increase in temperature, and change in composition.
Solidification refers to the process by which molten magma is converted into solid by cooling down of temperature.
If solidification occurs below the earth surface the rock is termed as intrusive rock whereas if the same occurs above the earth surface the rock is termed as an extrusive rock
