Litton, Roger A., 1944-, author
Avebury, 1990
Buku Teks
Crawford, Adam
Longman, 1998
Buku Teks
O`Block, Robert L., author
Mosby, 1981
Buku Teks
editor by Michael Chaney; Alan F. MacDougall
Gower Publishing, 1994
Buku Teks
Crawford, Adam
Longman, 1998
Buku Teks