Peter, Chris Maina
Greendwood Press, 1990
Buku Teks
Selby, David, author
Cambridge University Press, 1988
Buku Teks
Murray, Rachel, author
Cambridge University Press, 2004
Buku Teks
edited by George Clack
[publisher not identified], 1998
Buku Teks
Nickel, James W., author
Blackwell , 2007
Buku Teks