The correct answer is option 'C' - Mud.

Golconda Fort, located in Hyderabad, India, was built before 1200. It was constructed using mud as the primary material. The use of mud as a building material was common in ancient times, especially in regions where other construction materials like stone or brick were not readily available.

Here is a detailed explanation of why Golconda Fort was made of mud:

1. Availability: Mud is abundantly available in many parts of India, including the region where Golconda Fort is situated. It was a convenient and cost-effective choice for constructing the fort.

2. Strength and Durability: Mud, when properly mixed with other materials, can become quite strong and durable. The mud used in the construction of Golconda Fort was often reinforced with organic materials like straw or animal dung, which increased its strength and prevented cracking.

3. Thermal Insulation: Mud has excellent thermal insulation properties, which helped in maintaining a comfortable temperature inside the fort. The thick mud walls acted as a natural barrier against the heat outside, keeping the interiors cool during hot summers.

4. Easy to Shape: Mud can be easily molded into various shapes and sizes, allowing for intricate architectural designs. The builders of Golconda Fort used mud to create elaborate arches, domes, and decorative elements, showcasing the artistic and engineering skills of that era.

5. Eco-Friendly: Mud is a sustainable and environmentally friendly building material. It is non-toxic, biodegradable, and does not produce harmful emissions during its production or use. Choosing mud as the primary material for constructing Golconda Fort was in line with the eco-friendly practices of ancient times.

In conclusion, Golconda Fort was made of mud, which was readily available, strong, durable, thermally insulating, easy to shape, and environmentally friendly. The use of mud as a construction material was a practical choice for the builders of Golconda Fort before 1200.