Harlow, Ralph Volney, author
Holt, Rinehart and Winston,Inc, 1964
Buku Teks
Tocqueville, Alexis De, author
Vintage Books, 1956
Buku Teks
Harper, Donald Victor
Prentice-Hall, 1982
Buku Teks
Sitkoff, Harvard, author
Oxford University Press, 2000
Buku Teks
Allen, Harry E.
Macmillan Publishing Company, 1989
Buku Teks