Swales, John M., author
Cambridge University Press, 2004
Buku Teks
edited by Paul N. Cheremisinoff, Robert P. Quellette
Pennsylvania Technomic , 1997
Buku Teks
Yin, Robert K., author
Sage, 2003
Buku Teks
Herbert, David T.
John Wiley & Sons, 1982
Buku Teks
Taylor, Griffith, author
Methuen, 1951
Buku Teks