Pageant Publishing, 2018
Majalah, Jurnal, Buletin
Pergamon Press, 2018
Majalah, Jurnal, Buletin
lafave, Wayne R.
Thomson Reuters, 2010
Buku Teks
Jefferson, Michael
Pitman, 1992
Buku Teks
Fletcher, George P., author
Oxford University Press, 2000
Buku Teks