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When Lü Bu was besieged by the allied forces of the warlords Cao Cao and Liu Bei at the Battle of Xiapi in 198 CE , Liu Bei 's general Guan Yu repeatedly made requests to Cao Cao , asking to marry Lady Du after their victory over Lü Bu .
 Lü Bu, Cao Cao, Liu Bei, Liu Bei, Guan Yu, Cao Cao, Lü Bu
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Lü Bu, Cao Cao, Liu Bei, Liu Bei, Guan Yu, Cao Cao, Lü Bu