Because 50%(46.98% in up and 3.71%) of total production of sugarcane occur in these two state. In these region transportation of raw material are also convienent which are generally bulky.

The correct answer is option C: Uttar Pradesh and Bihar.

Explanation:
- Sugar production is a significant agricultural activity in India, and sugar mills play a crucial role in processing sugarcane into sugar.
- The distribution of sugar mills across states in India is not uniform, with certain states having a higher concentration of mills than others.
- Uttar Pradesh and Bihar are the states where the majority of sugar mills are concentrated, accounting for sixty percent of the total mills in India.
- Let's explore these states in more detail.

Uttar Pradesh:
- Uttar Pradesh, located in northern India, is the leading state in terms of sugar production.
- It has a favorable climate and fertile soil, which makes it suitable for sugarcane cultivation.
- The state has a long history of sugarcane cultivation and has a high number of sugar mills.
- Some of the major sugar-producing regions in Uttar Pradesh include Meerut, Saharanpur, Moradabad, Bareilly, and Gorakhpur.
- The favorable agro-climatic conditions, availability of irrigation facilities, and government support have contributed to the concentration of sugar mills in this state.

Bihar:
- Bihar, located in eastern India, is also a significant contributor to the sugar industry.
- The state has favorable soil and climatic conditions for sugarcane cultivation.
- Bihar has a long tradition of sugarcane farming, and many farmers rely on it as a source of income.
- Major sugar-producing regions in Bihar include West Champaran, East Champaran, Vaishali, and Sitamarhi.
- The state government has also taken initiatives to promote the sugar industry and provide support to sugar mills.
- These factors have led to the concentration of sugar mills in Bihar.

Summary:
- Uttar Pradesh and Bihar are the states where the majority of sugar mills are concentrated in India.
- These states have favorable agro-climatic conditions, a long history of sugarcane cultivation, and government support, which have contributed to the growth of the sugar industry in these regions.