Bengtsson, Ann McDonagh, author
Gower, 1992
Buku Teks
Reynolds, Amanda, author
Open universtity press , 2000
Buku Teks
Shiver, John M., author
Jones & Bartlett Learning, 2016
Buku Teks
edited by Allan McNaught
Chapman and Hall , 1991
Buku Teks
Goodwin, Nick, author
McGraw-Hill Open Univ. Press, 2006
Buku Teks