The Subansiri river is a tributary of the:

The correct answer is: c) Brahmaputra.

The Subansiri River is a tributary of the Brahmaputra River in India and China. It is the longest tributary of the Brahmaputra, with a length of 510 kilometers (317 miles). The Subansiri River originates in the Himalayas in Tibet, and flows through the Indian states of Arunachal Pradesh and Assam. It joins the Brahmaputra River near the town of Dibrugarh in Assam.

The Subansiri River is a major source of water for irrigation and hydroelectric power in India. It is also a popular destination for fishing and rafting.

The other options are incorrect because:

• The Barak River is a tributary of the Meghna River in Bangladesh.
• The Dhansiri River is a tributary of the Brahmaputra River in India.
• The Manas River is a tributary of the Brahmaputra River in India and Bhutan.