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Keijo Aarre Virtanen , ( 28 August 1945 in Naantali ) , is a Finnish historian , PhD 1980 .
 Keijo, Virtanen, Naantali, Finnish
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Keijo, Virtanen, Naantali, Finnish