Correct Option: B

Kosi is known as the "Sorrow of Bihar", as it has caused widespread human suffering in the past due to flooding and very frequent changes in course, when it flows from Nepal to Bihar. Over the last 250 years, the Kosi River has shifted its course over 120 km from east to west. Its unstable nature has been attributed to the heavy silt it carries during the monsoon season and flooding in India has extreme effects.