The correct answer is: A. limestone and clay.
Cement is a binding agent that is used to hold together other materials, such as concrete, mortar, and plaster. It is made by strongly heating a mixture of limestone and clay. The heat causes the limestone to decompose into calcium oxide and carbon dioxide. The clay also decomposes, forming silica, alumina, and iron oxide. These materials then react with each other to form cement clinker. The clinker is ground into a powder and mixed with water to form cement.
Limestone is a sedimentary rock that is composed of calcium carbonate. It is the most common type of rock in the world. Clay is a fine-grained sedimentary rock that is composed of clay minerals. Clay minerals are hydrous aluminum silicates. They are the main component of soils and are used in a variety of industrial applications.
The other options are incorrect because they do not contain limestone. Chalk is a type of limestone that is composed of calcium carbonate. Graphite is a form of carbon.