Drate, Spencer
North Light Books, 1999
Buku Referensi
Lee, Min-young
Mizan, 2014
Buku Teks SO
Winnington, Alan
Seven Seas Publishers, 1962
Buku Teks SO
edited by Tracey Skelton, Gill Valentine
Routledge , 1998
Buku Teks SO
Agus Sunarto, Rudy Silalahi, Tarno Darwan, translator
Internews -- Indonesia, 2001
Buku Teks