Ramage, Janet, 1932-
Oxford University Press, 1983
Buku Teks SO
Rukl, Antonin
Sterling Publishing Co., 1999
Buku Referensi
Hecht, Jeff
McGrawHill, 1986
Buku Referensi
Baghdad Summer Resorts & Tourism Service 1961
Buku Teks
Summer Ressorts & Tourism Service, 1961
Buku Teks SO