Gorman, Michael
Libraries Unlimited, 1990
Buku Teks SO
Association for Civil Society Development in azerbaijin, 2008
Majalah, Jurnal, Buletin
Vance, Charles C.
McGraw-Hill, 1974
Buku Teks
Nasution, Abdul Haris, 1918-2000
Seruling Masa, 1971
Buku Teks
Ahuja, B. N.
Surjeet Publications, 1989
Buku Teks SO