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The " " trusty system " " ( sometimes homophonically but incorrectly called " trustee system " ) was a penitentiary system of discipline and security enforced in parts of the United States until the 1980 s , in which designated inmates were used by prison staff to control and administer physical punishment to other inmates according to a strict , prison-determined , inmate hierarchy of power .
 United States
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 United States