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In 1974 , Dio sang on the Roger Glover conducted and produced concept album " The Butterfly Ball and the Grasshopper 's Feast " .
 Dio, Roger Glover
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Dio, Roger Glover