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Marks attended Yale University from 1911 to 1915 then served as an officer in the United States Marine Corps during World War I , receiving the Silver Star and two Purple Heart s. After the war , in 1923 , he earned his PhD at the University of Chicago in History , writing his dissertation on the Spanish-American War .
 Marks, Yale University, United States Marine Corps, University of Chicago
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Marks, Yale University, United States Marine Corps, University of Chicago