Answer: A. When magma cools and solidifies
Explanation: Igneous rocks form when magma cools and solidifies. This could occur on a volcano or on Earth’s surface, though it must be noted that all magma develops underground. Similar to lava, magma is molten rock that is underground. A way to remember how igneous rocks are formed is by remembering that the term is derived from the Latin word for fire, which can remind you of magma.