The largest river system in Nagaland is the:

Dhansiri
Barak
Tizu
Doyang

The correct answer is: d) Doyang.

The Doyang River is the largest river system in Nagaland, India. It originates in the Patkai Hills and flows through the districts of Wokha, Mokokchung, and Tuensang before joining the Brahmaputra River in Assam. The Doyang River is a major source of irrigation and drinking water for the people of Nagaland. It is also a popular destination for fishing and boating.

The Dhansiri River is a tributary of the Brahmaputra River. It originates in the Naga Hills and flows through the districts of Golaghat, Jorhat, and Sivasagar in Assam. The Dhansiri River is a major source of irrigation and drinking water for the people of Assam. It is also a popular destination for fishing and boating.

The Barak River is a tributary of the Brahmaputra River. It originates in the Manipur Hills and flows through the districts of Cachar, Karimganj, and Hailakandi in Assam. The Barak River is a major source of irrigation and drinking water for the people of Assam. It is also a popular destination for fishing and boating.

The Tizu River is a tributary of the Brahmaputra River. It originates in the Patkai Hills and flows through the districts of Mon and Tuensang in Nagaland. The Tizu River is a major source of irrigation and drinking water for the people of Nagaland. It is also a popular destination for fishing and boating.