Hailey
Macmillan, 1950
Buku Teks
Coulmas, Florian
B. Blackwell, 1989
Buku Teks
Palmer, R.R. (Robert Roswell), 1909-2002, author
McGraw-Hill, 1992
Buku Teks
National Geographic Book Service
National Geographic Society, 1988
Buku Referensi
Joseph Reither, editor
The New Home Library, 1942
Buku Teks