APA (7th ed.) Zitazioa
United States Postal Service. History of the United States Postal Service: 1775-1993.
Chicago Style (17th ed.) Zitazioa
United States Postal Service. History of the United States Postal Service: 1775-1993.
MLA (9th ed.) Zitazioa
United States Postal Service. History of the United States Postal Service: 1775-1993.
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