The correct answer is - A. Magma solidifies slowly, resulting in a coarse-grained texture.
The intrusive igneous rocks are forming when the magma solidifies very slowly, deep underground, under higher temperatures and pressures. All these conditions contribute to the coarse-grained structure to form on these types of rocks and have it as a trademark. These rocks are very hard rocks, with big density, their colors vary a lot but are more on the dark side usually. Some of them are diorite, granite, pegmatite...