Answer: C
Correct answer: Tripura
The Seven Sisters are Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland and Tripura. Sikkim, added later and connected to the rest only through the narrow Siliguri corridor, is often called the brother. They are joined to the rest of India by that corridor alone - the Chicken’s Neck - barely 22 km wide at its narrowest, which gives the region both its strategic sensitivity and much of its economic isolation. Around 98 per cent of the region’s boundary is international, with China, Myanmar, Bangladesh and Bhutan. The region is exceptionally diverse ethnically and linguistically, and much of it is governed under the Sixth Schedule, which provides for autonomous district councils in the tribal areas of Assam, Meghalaya, Tripura and Mizoram. Several states also have special provisions under Article 371. West Bengal, Odisha and Bihar are eastern states, but not part of the group.