The correct answer is B. Hiuen-Tsang.
Hiuen-Tsang was a Chinese Buddhist monk who traveled to India in the 7th century CE to study at Nalanda University. He was one of the most famous pilgrims to India and his writings provide valuable insights into the history and culture of the subcontinent at that time.
Megasthenes was a Greek ambassador to India in the 4th century BCE. He wrote a detailed account of his travels in India, which is an important source of information about the Mauryan Empire.
Ibn Battuta was a Moroccan traveler who visited India in the 14th century CE. He wrote a travelogue about his experiences, which is an important source of information about the Delhi Sultanate.
Al-Biruni was a Persian scholar who visited India in the 11th century CE. He wrote a number of works on Indian history, culture, and religion, which are important sources of information about the subcontinent at that time.
Hiuen-Tsang was the only one of the four who was a student of Nalanda University.