The correct answer is A. West Champaran.
West Champaran is a district in the Indian state of Bihar. It is located in the northwestern part of the state, and is bordered by Nepal to the north, Uttar Pradesh to the west, and the districts of East Champaran, Sitamarhi, and Muzaffarpur to the south and east. The district has a population of over 4 million people, and its headquarters is the town of Bettiah.
West Champaran is a major agricultural district, and is known for its production of rice, wheat, sugarcane, and maize. The district is also home to a number of industries, including sugar mills, rice mills, and textile mills.
West Champaran is a historically significant district. It was the site of the Champaran Satyagraha, a major protest movement led by Mahatma Gandhi in 1917. The movement was successful in securing better working conditions for the indigo farmers of the district.
Siwan, Gopalganj, and Madhubani are all districts in Bihar, but they do not border Nepal.