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Under whom this " Master of the Marble Madonnas " might have received his training is unknown but it surely would have been in the workshop of one of these masters .
 Master, Marble Madonnas
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Master, Marble Madonnas