Sanders, Thomas H.
Harvard. Univ., Press, 1951
Buku Teks
Heckert, J. Brooks (Josiah Brooks), 1893-, author
Ronald Press, 1953
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Mace, Myles L.
Harvard University , 1950
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Cheeks, James E.
Dow Jones-Irwin , 1974
Buku Teks
Chew, Sally
Times Books International, 1995
Buku Teks