Explanation:

The correct answer to the question is option 'b' i.e. Cotton.

Ginning mill is a factory or a unit where the process of ginning is done. Ginning is the process of separating cotton fibers from the seeds. In this process, the cotton is processed in order to remove impurities and prepare it for further use in the textile industry.

Key points:
- Ginning mills primarily deal with raw cotton.
- They purchase cotton from cotton farmers or cotton traders.
- Cotton is the main raw material for ginning mills to produce cotton fibers.
- These cotton fibers are then used in the production of various textile products like yarn, fabric, and clothing.

Process of ginning:
1. Cotton is brought to the ginning mill in the form of bales.
2. The bales are opened and the cotton fibers are separated from the seeds.
3. The seeds are collected separately as a byproduct, which is used for various purposes like oil extraction or animal feed.
4. The cotton fibers are further processed and cleaned to remove any impurities.
5. The cleaned cotton fibers are then packed and sold to textile mills or spinning mills.
6. The textile mills or spinning mills use these cotton fibers to produce yarn or thread, which is further used in the production of fabrics and clothing.

Role of ginning mill:
- The primary role of a ginning mill is to separate cotton fibers from the seeds.
- It ensures that the cotton fibers are clean and free from any impurities.
- The ginning mill plays a crucial role in the cotton supply chain as it provides the raw material for the textile industry.
- The quality of cotton produced by a ginning mill determines the quality of the final textile products.

In conclusion, the ginning mill buys cotton as its primary raw material. The cotton is processed to separate the fibers from the seeds, and these fibers are then used in the production of various textile products.