Correct answer: A. Xuanzang described India during Harsha's period
Explanation: Direct answer: Option A, Xuanzang described India during Harshavardhana’s period. Xuanzang, also written Hiuen Tsang, was a Chinese Buddhist monk and traveller who came to India in the seventh century CE. He studied Buddhist teachings, visited important places, and observed society, administration, education, religion, and towns. He spent time at the court of Harshavardhana, so his travel account is an important source for understanding India during Harsha’s reign. Option A is correct because it identifies the historical value of his connection with Harsha. Option B is wrong: the Taj Mahal was built much later under Mughal emperor Shah Jahan, not by Xuanzang. Option C is wrong: Maratha Swaraj belongs to the seventeenth-century history of Shivaji and the Marathas. Option D is wrong: the Delhi Sultanate began centuries later and was not founded by this traveller. Remember the chain: Xuanzang, seventh century, Harsha, travel account.