Hodgman, Donald R.
Harvard University Press, 1954
Buku Teks
Zagoria, Donald S.
Princeton University press, 1962
Buku Teks
Matthews, Donald R.
The University of North Carolina Press, 1960
Buku Teks
R. Conquest
Macmillan & CO LTD, 1960
Buku Teks
McGraw-Hill, 1955
Buku Referensi