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Pre-1950 Tibet has been described as a society in which the concept of human rights was unknown : it was ruled by a theocracy , beset by serfdorm and a form of slavery , had a caste-like social hierarchy , lacked a proper judicial system and enforced penal mutilations .
 Tibet
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Tibet