The correct answer is C. Three.
The rocks of Bihar are classified structurally into three types: igneous, sedimentary, and metamorphic.
Igneous rocks are formed when magma or lava cools and solidifies. Sedimentary rocks are formed when sediments, such as sand, mud, and pebbles, are compacted and cemented together. Metamorphic rocks are formed when existing rocks are subjected to heat and pressure.
The three types of rocks can be distinguished by their appearance, texture, and composition. Igneous rocks are typically hard and dense, with a crystalline appearance. Sedimentary rocks are typically layered, with a variety of textures and compositions. Metamorphic rocks are typically hard and dense, with a banded or foliated appearance.
The rocks of Bihar are important because they provide a record of the geological history of the region. They also provide resources such as coal, iron ore, and limestone.