The correct answer is (c). Arunachal Pradesh is a mountainous region in the eastern Himalayas. It is the largest state in India by area, but has the lowest population density. The state is home to a diverse range of ethnic groups and languages. The climate is tropical in the lowlands and temperate in the highlands. The economy is based on agriculture, forestry, and tourism.
(a) is incorrect because Arunachal Pradesh is not a desert region. The state receives an average annual rainfall of over 2,000 mm.
(b) is incorrect because Arunachal Pradesh is not a coastal region. The state is landlocked and does not have any coastline.
(d) is incorrect because Arunachal Pradesh is not a plain region. The state is mountainous and has a rugged terrain.