The correct answer is option 4, Ayodhya and Janakpur. In May 2018, bus service was launched between Ayodhya, a city in the Indian state of Uttar Pradesh, and Janakpur, a city in Nepal.
Option 1, Nalanda and Lumbini, is incorrect. Although both Nalanda and Lumbini are historically significant places, there is no record of a bus service being launched between these two places in May 2018.
Option 2, Gaya and Kathmandu, is also incorrect. Gaya is another city in the Indian state of Bihar, known for its religious significance to both Hindus and Buddhists. Although there are bus services between Gaya and Kathmandu, it is not the answer to the given question.
Option 3, Varanasi and Vaktapur, is again incorrect. Varanasi is a major city in Uttar Pradesh, famous for its religious importance, while Vaktapur is a city in Nepal. There is no record of a bus service being launched between these two places in May 2018.
Therefore, the correct answer is option 4, Ayodhya and Janakpur.