Kennan, George F., 1904-
Princeton University Press , 1954
Buku Teks SO
Perkins, Dexter
Harvard University Press, 1954
Buku Teks SO
McCormick, James M.
Thomson, 2005
Buku Teks SO
Herrick, Christopher
Longman, 2003
Buku Teks SO
Langdon, Robert M.
Littlefield Adams, 1961
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