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He played tennis throughout his time there , participating in the 1952 U.S. National Championships , 1953 U.S. National Championships , 1954 U.S. National Championships , 1955 U.S. National Championships , 1956 U.S. National Championships , and 1957 U.S. National Championships .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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