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Tony Lucki , a former non-executive director of Riverdeep , remained in his position as Houghton Mifflin 's chief executive officer .
 Riverdeep, Houghton Mifflin
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Riverdeep, Houghton Mifflin