The Tawang district of Arunachal Pradesh is known for its significant:

Buddhist monastery
Tea plantations
Wildlife sanctuary
Oil reserves

The correct answer is: a) Buddhist monastery.

Tawang is a district in the Indian state of Arunachal Pradesh. It is the largest district in the state by area. The district is known for its significant Buddhist monastery, the Tawang Monastery. The monastery is the seat of the 6th Dalai Lama, Tsangyang Gyatso. It is one of the largest monasteries in India and is a popular tourist destination.

The other options are incorrect. Tea plantations are not a significant feature of Tawang district. Wildlife sanctuaries are also not a significant feature of the district. Oil reserves are not found in Tawang district.