The correct answer is D. Extrusive igneous rocks cool and solidify at the Earth's surface, while intrusive igneous rocks cool and solidify below the Earth's surface.
Explanation
Igneous rocks, also called magmatic, are all rocks that are formed by the solidification of magma. However, igneous rocks are classified into two groups. First are the plutonic or intrusive igneous rocks that are the result of the solidification of magma within the lithosphere. Secondly, there are the volcanic or extrusive igneous rocks that are the result of the cooling of magma that occurs at the surface or a shallow depth (in whole or in part). According to the above definition, the difference between these two types of rocks is that extrusive igneous rocks cool and solidify on the Earth's surface, while intrusive igneous rocks cool and solidify below the Earth's surface. So the correct answer is D.