The correct option is A libraries
The ancient Nalanda was a center of learning from the 5th century CE to 12th century CE, located in present-day Rajgir, Bihar, India. Nalanda was one of the oldest universities in the world, and UNESCO declared the ruins of Nalanda Mahavihara a world heritage site. Its book repository area was known as Dharmagunj, which has three multi-story buildings named Ratna Sagara, Ratna Nidhi, and Ratna Ranjana.