Drate, Spencer
North Light Books, 1999
Buku Referensi
edited by Tracey Skelton, Gill Valentine
Routledge , 1998
Buku Teks SO
Agus Sunarto, Rudy Silalahi, Tarno Darwan, translator
Internews -- Indonesia, 2001
Buku Teks
Shanks, Bob
Vintage Books, 1977
Buku Teks SO
Winnington, Alan
Seven Seas, 1962
Buku Teks SO