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Senator Mason 's son , Armistead Thomson Mason , of Selma , was shot and killed by his cousin , John Mason McCarty , in a duel fought at the Bladensburg dueling grounds in Bladensburg , Maryland , in February 1819 .
 Mason, Armistead Thomson Mason, Mason, Bladensburg, Bladensburg, Maryland
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Mason, Armistead Thomson Mason, Mason, Bladensburg, Bladensburg, Maryland