The correct answer is: C. Columns and struts
Cast iron is a type of iron that is made by melting iron and then pouring it into a mold. It is a strong and durable material that is often used in construction. Cast iron is used for columns and struts because it is strong and can support a lot of weight. It is also resistant to corrosion, which makes it a good choice for use in outdoor applications.
Option A is incorrect because cast iron is not typically used for structural works in beams. Beams are structural elements that support the weight of a building or other structure. They are typically made from steel or concrete, which are stronger materials than cast iron.
Option B is incorrect because cast iron is not typically used for small sized water pipes. Water pipes are typically made from PVC, copper, or steel, which are all more corrosion-resistant materials than cast iron.
Option D is incorrect because cast iron is used for columns and struts.