Concept:Rocks formed by cooling and solidification of magma within the Earth's crust are called intrusive igneous rocks, commonly known as plutonic rocks.Explanation:Magma that remains inside the Earth's crust cools slowly.Slow cooling allows large crystals to form.Such rocks are called plutonic or intrusive igneous rocks.Extrusive rocks form when lava cools on the Earth's surface.Metamorphic and sedimentary rocks are not formed by solidification of magma.Answer:A. Plutonic rock