The correct answer is: a) Affordable public transportation.
SNT buses are a popular mode of transportation in Sikkim, connecting major towns and villages across the state. They are a reliable and affordable way to get around, and offer a variety of routes to choose from. The buses are also comfortable and well-maintained, making them a good option for both locals and tourists.
Option b) is incorrect because SNT buses are not luxury travel options. They are a basic form of public transportation, and do not offer the same level of comfort or amenities as private taxis or tour buses.
Option c) is incorrect because SNT buses have a wide route coverage. They connect major towns and villages across the state, and there are many different routes to choose from.
Option d) is incorrect because SNT buses have a regular schedule. The buses depart from their respective stations at specific times, and there are no frequent schedule changes.