The correct answer is: Nalanda.
Nalanda district is home to a concentration of ancient Buddhist sites, including the ruins of the Nalanda Mahavihara, a Buddhist monastery complex that was once one of the most important centers of learning in the world. The Nalanda Mahavihara was founded in the 5th century CE and flourished for over 700 years. It was destroyed by the Muslim invaders in the 12th century CE.
The other options are incorrect because they do not have a concentration of ancient Buddhist sites. Gaya is a district in Bihar that is home to the Mahabodhi Temple, a UNESCO World Heritage Site. Vaishali is a district in Bihar that is home to the ruins of the ancient city of Vaishali, which was one of the capitals of the Vajji confederacy. West Champaran is a district in Bihar that is home to the Champaran Satyagraha, a major event in the Indian independence movement.
The Nalanda Mahavihara was a Buddhist monastery complex located in the Indian subcontinent. It was one of the most important centers of learning in the world from the fifth to twelfth centuries. The Mahavihara was destroyed by the Muslim invaders in 1197.
The Nalanda Mahavihara was founded in the fifth century by the Gupta emperor Kumaragupta I. It was built on the site of an earlier monastery that had been founded by the Buddha himself. The Mahavihara was initially a small monastery, but it grew rapidly in size and importance over the next few centuries.
The Mahavihara was home to thousands of monks and scholars from all over the world. It was a center of learning for both Buddhist and non-Buddhist subjects. The Mahavihara was also a center of Buddhist missionary activity.
The Mahavihara was destroyed by the Muslim invaders in 1197. The invaders killed many of the monks and scholars, and they destroyed the buildings and libraries of the Mahavihara. The Mahavihara has never been rebuilt.
The ruins of the Nalanda Mahavihara are located in the Nalanda district of Bihar, India. The ruins are a UNESCO World Heritage Site. The ruins of the Mahavihara are a popular tourist destination.