The correct answer is D. In all the districts.
District Registration and Counselling Centres have been established in all the districts of Bihar. These centres are responsible for registering and counselling students who are interested in taking the National Eligibility cum Entrance Test (NEET). The centres also provide information about the NEET exam and the admission process to various medical colleges in the country.
Option A is incorrect because Patna is only one of the districts in Bihar where a District Registration and Counselling Centre has been established.
Option B is incorrect because Bhagalpur is only one of the districts in Bihar where a District Registration and Counselling Centre has been established.
Option C is incorrect because Buxar is only one of the districts in Bihar where a District Registration and Counselling Centre has been established.