Explanation:

- Hiuen Tsang: Correct Answer. Hiuen Tsang was a Chinese Buddhist monk who visited India in the 7th century. He wrote detailed accounts of his travels, and he mentioned that Dhruvasena II attended Harsha’s assembly at Prayag.

- Marco Polo: An Italian merchant known for his travels to Asia but lived much later, in the 13th century. He didn't write about events from Harsha's time.

- Fa-Hien: A Chinese Buddhist monk who visited India earlier, in the 5th century. His writings are valuable but do not cover Harsha’s era.

- Itsing: Another Chinese Buddhist monk who traveled to India, but his journey occurred after Harsha’s time.