Lonely planet, [date of publication not identified]
Buku Referensi
Marzuki Usman, author
HL, 1999
Buku Teks
Liffers, Lutz, author
Edition Temmen, 2008
Buku Referensi
DuBrin, Andrew J., author
Prenada Media Group, 2009
Buku Teks
Hayrettin Kardestuncer, editor-in-cheif
McGraw-Hill, 1987
Buku Referensi