The article from nps.gov is a primary source, while William Still's diary entry is a secondary source.
Primary Source: The article "Harriet Tubman and the Underground Railroad" retrieved from nps.gov, dated March 11, 2017, is a primary source.
Secondary Source: The digital print of an entry from the diary of William Still, an African American abolitionist living from 1821 to 1902, is a secondary source.
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