Explanation:

The Teesta River: It is the right-bank tributary of the Brahmaputra river. The Teesta rises from Zemu glacier in Kanchenjunga massif in Sikkim. The Teesta river drains the entire state of Sikkim and a part of Darjeeling Hills. It is known as the lifeline of Sikkim. The Teesta flows along a very deep gorge which divides north Bengal or the hills of Darjeeling into two parts-Tiger Hill range in the west and the Kalimpong Hill range in the east. It joins the Brahmaputra on its right-bank in Bangladesh.