Lutz, William D., author
Cambridge University Press, 1994
Buku Referensi
Gutteridge, Anne C.
Cambridge University Press, 1983
Buku Referensi
edited by Robert L. Chapman
Collins, 1989
Buku Referensi
Geddes & Grosset, 2000
Buku Referensi
Geddes & Grosset, 2003
Buku Referensi