Hawley, Georgina, author
Social Science Press, 1997
Buku Teks
Morgan, Derek, author
Cavendish, 2001
Buku Teks
Albert, Ethel M., author
American Book Company, 1953
Buku Teks
Smith, Michael, author
Cambridge University Press , 2004
Buku Teks
Pojman, Louis P., author
Wadsworth and Cengage Learning, 2012
Buku Teks