Hint: Nalanda was a Mahavihara, a large Buddhist monastery, in the ancient kingdom of Magadha. They reportedly mentioned the Harsha for patronising the Nalanda during the great age of the Guptas. Further, it was prized and cherished by the Palas. Vikramashila was one of the two most important centres of learning in ancient India, along with Nalanda. Vikramashila was one of the largest Buddhist universities than capital cities mainly due to the fact that there was a demand from the people of those cities to establish capital there.
Complete answer: Nalanda and Vikramshila were the two most important centres of learning in India during the Pala Empire. During the year 1193, an army led by the Turkish leader Bakhtiyar Khilji, the general of sultan Qutubuddin Aibak destroyed these two.
Additional Information: Bakhtiyar Khilji was known as the Indian scholar and teacher famous for the doctors of his court. He decided to destroy the roots of the knowledge with Buddhism and Ayurveda. He set the fire to the great library of Nalanda. Further, he burned down nearly 9 million manuscripts.
Thus the correct option is C.
Note: Nalanda University was destroyed three times by different invaders. The first destruction was caused by the Huns under the reign of Mihirakula. The second destruction came during the 7th century by the Goudas. This time, the Buddhist king Harshavardhana then restored the university. The third attack came on the Nalanda University by the Muslim army was most destructive. It was led by the Turkish leader Bakhtiyar Khilji during the year 1193.