The Yangtze River originates from the main peak of Tanggula on the Qinghai-Tibet Plateau, and its main stream flows through 1 1 provincial administrative units such as Qinghai and Tibet, and finally flows into the East China Sea. The Yangtze River is more than 6,300 kilometers long, with a drainage area of 1 0.8 million km2 and an annual runoff of about 1 100 million m3, accounting for1of the national annual runoff.
Therefore, choose: B.