The correct answer is: b) Rural areas.
Arunachal Pradesh is a state in northeastern India. It is the largest state in India by area, but it has the lowest population density. The majority of the population of Arunachal Pradesh lives in rural areas. This is because the state is mountainous and has a difficult terrain. The main occupation of the people in rural areas is agriculture.
The other options are incorrect. Option a) is incorrect because only a small percentage of the population of Arunachal Pradesh lives in urban areas. Option c) is incorrect because the majority of the population of Arunachal Pradesh does not live in high altitude regions. Option d) is incorrect because Arunachal Pradesh does not have any coastal plains.