Edited by Kevin McConway and Basiro Davey
Open UNiversity Press, 2003
Buku Teks
Westview Press, 1980
Buku Teks
Krickeberg, Klaus, author
Springer, 2012
eBooks
Webber, Roger, author
Cab International, 1996
Buku Teks
Fos, Peter J., author
Jossey- Bass, 2011
Buku Teks