Option a is the correct answer. Nalanda is the most ancient monastery in Bihar. The history of Nalanda, the ancient university town of Bihar, goes back to the days of Buddha and Mahavira in the sixth century BC. However, excavations have not revealed anything to suggest that the site was occupied before the Gupta period (fifth century A.D.). Kumaragupta was the first to donate to Nalanda monastery. Buddha Gupta, Tathagata Gupta, and Baladitya also donated to the monastery after him. Important Tips Bhaja caves: Bhaja is the ancient monastery in India, which dates back to the 2nd century BCE. Bhaja is a complex of rock-cut caves located near Lonavala in Maharashtra. Bhaja was a Buddhist monastery that belonged to the Hinayana sect. Bhaja has 22 caves, which include chaityas (prayer halls), viharas (residences), and stupas (relics). Bhaja is famous for its artistic and architectural features, such as the carved pillars, the wooden beams, the vaulted ceilings, the sculptures, and the paintings. Bhaja is also a UNESCO World Heritage Site.