The correct answer is: c) Umngot River.
The Umngot River is a river in the East Khasi Hills district of Meghalaya, India. It is a tributary of the Brahmaputra River. The river is navigable for some stretches, and is a popular tourist destination.
The Brahmaputra River is the largest river in India and the third largest river in Asia. It is a trans-boundary river, flowing through India, Bangladesh, and China. The river is not navigable for most of its length, due to its rapids and waterfalls.
The Barak River is a river in the Barak Valley region of Assam, India. It is a tributary of the Brahmaputra River. The river is navigable for some stretches, and is a major transportation route in the region.
The Kynshi River is a river in the East Khasi Hills district of Meghalaya, India. It is a tributary of the Umngot River. The river is not navigable, due to its rapids and waterfalls.