The correct answer is: a) The Duars.
The Duars are a hilly region located in the eastern Himalayas, in the Indian state of Assam. They lie to the north of the Brahmaputra River and are part of the Eastern Himalayan biodiversity hotspot. The Duars are a popular tourist destination, known for their natural beauty and wildlife.
The Terai is a lowland region located in the foothills of the Himalayas, in the Indian states of Uttarakhand, Uttar Pradesh, Bihar, Jharkhand, and West Bengal. It lies to the south of the Brahmaputra River and is part of the Indo-Gangetic Plain. The Terai is a densely populated region, home to a variety of ethnic groups.
The Barak Valley is a valley located in the northeastern Indian state of Assam. It is bounded by the Brahmaputra River to the north, the Meghalaya Hills to the south, and the Manipur Hills to the east. The Barak Valley is a fertile region, home to a variety of crops, including rice, tea, and jute.
The Deccan Plateau is a plateau located in the southern Indian subcontinent. It is the largest plateau in India, covering an area of over 1.5 million square kilometers. The Deccan Plateau is a geologically stable region, with a long history of human habitation.