The Brahmaputra Valley region in Arunachal Pradesh is primarily a:

The correct answer is: a) Hilly region.

The Brahmaputra Valley region in Arunachal Pradesh is a hilly region. It is located in the eastern part of the state and is bounded by the Himalayas to the north, the Patkai Hills to the south, and the Brahmaputra River to the east. The region is characterized by its rugged terrain, with mountains, hills, and valleys. The climate is tropical monsoon, with hot, humid summers and cool, dry winters. The main crops grown in the region are rice, maize, and wheat. The region is also home to a number of ethnic groups, including the Adi, Mishmi, and Nyishi.

The other options are incorrect because:

• Option b, “Mountainous region”, is incorrect because the Brahmaputra Valley region is not as mountainous as other parts of Arunachal Pradesh, such as the Eastern Himalayas.
• Option c, “Plateau region”, is incorrect because the Brahmaputra Valley region is not as high as other plateau regions in India, such as the Deccan Plateau.
• Option d, “Plain region”, is incorrect because the Brahmaputra Valley region is not as flat as other plain regions in India, such as the Indo-Gangetic Plain.