Nagel, Stuart S.
The University of Alabama Press, 1984
Buku Teks
Howlett, Michael, author
Oxford University Press, 2009
Buku Teks
Bozeman, Barry, author
St. Martin's Press, 1979
Buku Teks
Helen Margetts, Perri 6, Christopher Hood, editors
Oxford University Press, 2012
Buku Teks
Weimer, David L., author
Pearson Prentice Hall, 1989
Buku Teks