The correct answer is: A. Gaya
Gaya is a city in the Indian state of Bihar. It is the headquarters of Gaya district and Gaya division. The city is situated on the banks of the Phalgu River, about 100 kilometers (62 mi) south of Patna, the capital of Bihar. Gaya is one of the oldest cities in India, and is mentioned in the Mahabharata and the Ramayana. The city is a major pilgrimage site for Hindus, Buddhists, and Jains.
The Prayag Prashasti is an inscription that was found in Prayag (Allahabad) in 1837. The inscription is dated to the 13th century CE, and is written in Sanskrit. The inscription records the achievements of the Delhi Sultan Balban.
The inscription states that Balban conquered many territories, including Gaya. This suggests that Gaya was included in Bihar at the time of Balban.
The other options are incorrect because they are not mentioned in the Prayag Prashasti.