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The B&P tunnel allowed the Pennsylvania Railroad ( PRR ) direct access to Washington , D.C. for the first time by connecting its Northern Central Railway affiliate ( which arrived in Baltimore from the north ) to the Baltimore and Potomac 's new spur , which ran to Washington .
 Pennsylvania Railroad, Washington , D.C., Baltimore, Baltimore, Potomac
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Pennsylvania Railroad, Washington , D.C., Baltimore, Baltimore, Potomac