The correct answer is (d). Doyang is not a major factor for water transportation in Nagaland.
Dhansiri, Dikhu, and Barak are all major rivers in Nagaland that are used for water transportation. Dhansiri is the longest river in Nagaland, flowing for 270 kilometers. It is a tributary of the Brahmaputra River. Dikhu is a tributary of the Dhansiri River. It flows for 150 kilometers. Barak is the largest river in the Barak Valley of Assam. It flows for 270 kilometers.
Doyang is a river in Nagaland that flows for 120 kilometers. It is a tributary of the Brahmaputra River. Doyang is not a major factor for water transportation in Nagaland because it is not navigable for most of its length. The river is also prone to flooding, which makes it difficult to use for transportation.