Bersihar Lubis, Rinold Thamrin, Kusfiardi
Yayasan Swadaya Mandiri, 2001
Buku Teks
Winters, Jeffrey A., author
Djambatan, 1999
Buku Teks
Artikel Jurnal
Routledge, Taylor & Francis Group, 2007
Buku Referensi
Hazel, John, author
Routledge, 2000
Buku Teks