Mott, Graham
Pitman, 1997
Buku Teks
Stillman, Richard N.
Holt, Rinehart and Wilson, 1962
Buku Teks
Departmen of Home Affairs ot the Republic Indonesia, 2008
Buku Referensi
Hudson, Alastair
Sweet & Maxwell, 2000
Buku Teks
McDaniels, John F.
The World Community Association, 1964
Buku Teks SO