Letter C. Limestone is the answer.
Limestone is one of the examples of a sedimentary rock which is composed largely of the aragonite, minerals and calcite that are different crystal forms of calcium carbonate or CaCO3. Most of these limestones are comprised of skeletal fragments of marine organisms such as forams, mollusks, and coral. Limestones make up 10% (approximately) of the total volume of all sedimentary rocks. Cave systems are mostly through limestone bedrock.