The correct answer is: Barak.
The Barak is the second-largest river in Assam after the Brahmaputra. It originates in the Manipur Hills and flows through the Barak Valley in Assam before joining the Brahmaputra near Karimganj. The Barak 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 Manas is a tributary of the Brahmaputra. It originates in the Himalayas and flows through the Manas National Park in Assam. The Manas is a popular destination for wildlife tourism.
The Kopili is a tributary of the Brahmaputra. It originates in the Khasi Hills and flows through the Kopili Valley in Assam. The Kopili is a major source of irrigation and drinking water for the people of Assam.
The Jiadhal is a tributary of the Barak. It originates in the Garo Hills and flows through the Garo Hills in Assam. The Jiadhal is a major source of irrigation and drinking water for the people of Assam.