The correct answer is D. All of the above.
Reinforced concrete is a composite material made of concrete and steel reinforcement. The concrete provides compressive strength, while the steel provides tensile strength. This combination of materials makes reinforced concrete very strong and durable.
Reinforced concrete is also very fire-resistant. Concrete is a non-combustible material, and the steel reinforcement will not melt until the concrete has reached a very high temperature. This makes reinforced concrete a good choice for buildings in areas with a high risk of fire.
Reinforced concrete is also very economical. It is a relatively inexpensive material to produce, and it can be used to create a wide variety of structures. The long lifespan of reinforced concrete also means that it is a cost-effective material in the long run.
In conclusion, the advantages of reinforced concrete are due to its monolithic character, fire-resisting and durability, and economy because of less maintenance cost.