The correct answer is: A. Una
Baba Balak Nath fair is held in Una district of Himachal Pradesh. It is a major Hindu pilgrimage site and is held every year in the month of May. The fair is dedicated to Baba Balak Nath, a Hindu saint who is believed to have lived in the 12th century. The fair is a week-long event and attracts thousands of pilgrims from all over India. The main attraction of the fair is the procession of the idol of Baba Balak Nath. The idol is taken out in a procession from the temple to the fair ground. The procession is accompanied by music, dancing and singing. The fair also has a number of stalls selling religious items, food and other items.
Option B, Kinnaur, is incorrect because the Baba Balak Nath fair is not held in Kinnaur. Kinnaur is a district in Himachal Pradesh and is known for its beautiful scenery and Buddhist monasteries.
Option C, Hamirpur, is incorrect because the Baba Balak Nath fair is not held in Hamirpur. Hamirpur is a district in Himachal Pradesh and is the headquarters of the Hamirpur district.
Option D, Shimla, is incorrect because the Baba Balak Nath fair is not held in Shimla. Shimla is the capital of Himachal Pradesh and is a popular tourist destination.