The correct answer is A. Chamba.
Sipi fair is a religious fair held in the Sipi Valley in Chamba district of Himachal Pradesh. It is held every year in the month of April or May. The fair is dedicated to the goddess Sipi Devi, who is worshipped by the people of the region. The fair is a major tourist attraction and is a good opportunity to experience the culture and traditions of the region.
Option B, Una, is incorrect because the Sipi fair is not held in Una district. Una is a district in Himachal Pradesh, but the Sipi fair is held in Chamba district.
Option C, Bilaspur, is incorrect because the Sipi fair is not held in Bilaspur district. Bilaspur is a district in Himachal Pradesh, but the Sipi fair is held in Chamba district.
Option D, Shimla, is incorrect because the Sipi fair is not held in Shimla. Shimla is the capital of Himachal Pradesh, but the Sipi fair is held in Chamba district.