The correct answer is D. All of the above.
The Kosi, Gandak, and Ghaghra are all navigable rivers in Bihar State. The Kosi is the largest river in Bihar, and it is a major source of irrigation and drinking water for the state. The Gandak is also a major river in Bihar, and it is a tributary of the Ganges River. The Ghaghra is a tributary of the Gandak River, and it is the third largest river in Bihar.
All three of these rivers are navigable for a significant distance, and they are used for transportation of goods and people. The Kosi is navigable for about 200 kilometers, the Gandak is navigable for about 150 kilometers, and the Ghaghra is navigable for about 100 kilometers.
These rivers are also important for fishing and tourism. The Kosi is known for its catfish, the Gandak is known for its carp, and the Ghaghra is known for its mahseer. These rivers are also popular destinations for boating, swimming, and fishing.
The Kosi, Gandak, and Ghaghra are all important rivers in Bihar State. They are a major source of irrigation and drinking water, and they are used for transportation, fishing, and tourism.