**Explanation:**

**Operation Flood** was a dairy development program launched in India in 1970. It aimed to increase milk production and make milk available to consumers at an affordable price. The program was implemented by the National Dairy Development Board (NDDB) and was successful in transforming India from a milk-deficient nation to one of the largest milk producers in the world.

**Production Increase:**

During Operation Flood, the production of milk in India increased significantly. The correct answer to the question is option 'C', which states that milk production increased fourfold. This means that the milk production increased by a factor of four.

**Reasons for the Increase:**

There were several factors that contributed to the increase in milk production during Operation Flood:

1. **Formation of Dairy Cooperatives:** Operation Flood focused on organizing small dairy farmers into cooperatives. These cooperatives provided farmers with access to resources such as modern technology, veterinary services, and financial assistance. This helped in increasing milk production at the grassroots level.

2. **Improved Breeding and Animal Health:** Operation Flood emphasized the improvement of cattle breeds through artificial insemination and crossbreeding. This resulted in the development of high-yielding breeds that produced more milk. Additionally, the program also focused on improving animal health by providing veterinary services and vaccinations, which reduced the mortality rate of cattle.

3. **Feed and Fodder Development:** Operation Flood aimed to increase the availability of nutritious feed and fodder for cattle. This was achieved through the promotion of scientific methods of fodder cultivation, such as silage making and hydroponics. The availability of good quality feed and fodder ensured better nutrition for the cattle, leading to increased milk production.

4. **Infrastructure Development:** Operation Flood also focused on the development of dairy infrastructure, such as milk collection centers, chilling plants, and processing units. This made it easier for farmers to sell their milk and ensured proper storage and processing, thereby reducing wastage and improving milk quality.

5. **Market Linkages:** Operation Flood established a network of milk cooperatives that procured milk from farmers and marketed it effectively. This ensured a fair price for the farmers and a steady supply of milk to consumers. The establishment of a well-organized market system helped in boosting milk production.

Overall, Operation Flood was successful in increasing milk production in India by implementing various strategies such as cooperative organization, improved breeding and animal health, feed and fodder development, infrastructure development, and market linkages. The fourfold increase in milk production during the program had a significant impact on the dairy industry and contributed to the socio-economic development of rural areas.