Explanation:

The Kosi is a trans-boundary river which flows through Tibet, Nepal and India.

• It has its source in Tibet that includes the world's highest upland; it then drains a large part of Nepal before emerging onto the Gangetic plains. 
• The river crosses into northern Bihar, India where it branches into distributaries before joining the Ganges near Kursela in Katihar district. 
• Its unstable nature has been attributed to course changes and the heavy silt it carries during the monsoon season, and flooding in India has extreme effects.
• The Kosi carries the maximum amount of silt and sand after the Brahmaputra in India.
• It is also known as the “Sorrow of Bihar” as the annual floods affect about 21,000 km2 of fertile agricultural lands thereby disturbing the rural economy. 

Hence all statements are correct.