Step 1: Understanding the Concept:
The query requires the identification of the buildings that comprised the great library of the ancient Nālandā Mahāvihāra (University).
Step 2: Detailed Explanation:
The library at Nālandā was known as the Dharma Gunj (Mountain of Truth). Historical accounts, particularly from Tibetan sources such as the writings of Taranatha, describe it as an extensive knowledge repository housed within three grand, multi-storied structures. The names of these three buildings were:
Ratnasāgara (Ocean of Jewels)
Ratnodadhi (Sea of Jewels)
Ratnarañjaka (Jewel-adorned)
These correspond to options (B), (D), and (C) respectively.
Consider option (A) Ratnakirti. Ratnakīrti was a prominent Buddhist philosopher and logician, primarily affiliated with Vikramaśīla University, and not a building at Nālandā.
Step 3: Final Answer:
The correct designations for the Nālandā library buildings are Ratnasāgara, Ratnarañjaka, and Ratnodadhi. Consequently, the option encompassing only (B), (C), and (D) is the accurate one.