Among the options given, option 4, Nalanda, has not yet been recognized as a World Heritage Site by UNESCO. While options 1, 2, and 3 (Ellora, Fatehpur Sikri, and Ajanta, respectively) have all been acknowledged by UNESCO as World Heritage Sites, Nalanda has not received this recognition. Nalanda, located in Bihar, India, is an ancient center of learning and a significant historical site. It was a renowned university in ancient India and played a vital role in the spread of Buddhism. Despite its historical and cultural significance, it has not yet been included in the list of UNESCO designated World Heritage Sites.