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In his only individual event , 200 m individual medley , Zatsepine challenged seven other swimmers on the final heat of seven , including top medal favorite Michael Phelps of the United States .
 Michael Phelps
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Michael Phelps