370183
Some committees specialize in specific stamp issues like the Washington-Franklin heads , the Prexie or the Liberty Series , while other committees study specialized areas of U.S. philately such as Plate Numbers and Marginal Markings , Private Vending and Affixing Perforations , Booklets and Panes , and Luminescence .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 None