 Complete the following phrase:  After Liu Beis conquest of Yi Province, he was able to supply his troops on his own, so Sun Quan sent Lu Su as an emissary to demand for the return of Jing Province, but Liu Bei refused. Sun Quan then sent Lü Meng and Ling Tong to lead 20,000 men to attack southern Jing Province and they succeeded in capturing Changsha, Guiyang, and Lingling commanderies. Meantime, Lu Su and Gan Ning advanced to Yiyang  with 10,000 men to block Guan Yu and took over command of the army at Lukou . Liu Bei personally went to Gongan County and Guan Yu led 30,000 men to Yiyang. When an all-out war was about to break out, the news that Cao Cao planned to attack 