Answer:
B. A body of igneous rock that forms within Earth's crust
Explanation:
Igneous rocks are of two types: intrusive and extrusive. The extrusive igneous rocks are formed by cooling of lava on the earth surface. The intrusive igneous rocks are formed when the magma cools down within the earth's crust. The intrusive rocks are also called as plutonic rocks. Hence, pluton is a body of an intrusive igneous rock.