Birdsall, Stephen S.
John Wiley & Sons, 1992
Buku Teks SO
Mittleman, Earl N.
New York University, [date of publication not identified]
Buku Teks SO
Gultom, Samuel
Greenwood Press, 1987
Buku Referensi
United States Information Agency, 1991
Buku Teks SO
Office of International Information Programs, 1991
Buku Teks SO