Concept:The Kosi River is called the "Sorrow of Bihar" because of its frequent and devastating floods that cause massive damage to life and property.Explanation:The river originates in Tibet and flows through Nepal before entering Bihar. It carries a heavy load of silt from the Himalayas, which raises its riverbed and causes it to frequently change its course. This unpredictability leads to widespread floods and displacement of millions. One of the worst floods occurred in 2008, affecting over 3 million people in Bihar. Hence, among the given options, only the Kosi River has earned this tragic title.Answer:C. Kosi