The correct answer is: a) The Duars.
The Duars are a narrow strip of plains at the foothills of the Himalayas in Assam. They are a part of the Brahmaputra Valley and are located between the Brahmaputra River and the Himalayas. The Duars are a fertile region and are home to a variety of crops, including rice, tea, and jute. They are also home to a number of ethnic groups, including the Bodo, the Garo, and the Khasi.
The Karbi Plateau is a plateau located in the central part of Assam. It is a hilly region and is home to a number of ethnic groups, including the Karbi, the Dimasa, and the Kuki.
The Brahmaputra Valley is a large valley located in the north-eastern part of India. It is a fertile region and is home to a number of ethnic groups, including the Assamese, the Bodo, and the Garo.
The Barak Valley is a valley located in the south-eastern part of Assam. It is a fertile region and is home to a number of ethnic groups, including the Bengali, the Karbi, and the Khasi.