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In 1932 he entered Yale University where he majored in Christian ethics under Richard Niebuhr , and received a Ph.D. in 1939 .
 Yale University, Richard Niebuhr
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Yale University, Richard Niebuhr