Reynolds, Amanda, author
Open universtity press , 2000
Buku Teks
edited by Allan McNaught
Chapman and Hall , 1991
Buku Teks
Goodwin, Nick, author
McGraw-Hill Open Univ. Press, 2006
Buku Teks
Porter-O`Grady, Tim, author
Mosby Elsevier, 2011
Buku Teks
Keen, Jeffrey S.
John Wiley & Sons, 1981
Buku Teks