Beneficial Management Institute, [Date of publication not identified]
Buku Teks
Learned, Edmund P. (Edmund Philip), 1900-1991
Andover Press, 1957
Buku Teks
Kranz, Rachel
Factsts On File, Inc, 2005
Buku Teks
Huxley, Julian
New American Library, 1957
Buku Teks
Buku Teks