Fitzpatrick, Tony, author
Palgrave Macmillan, 2005
Buku Teks
Finston, Harmon L., author
John Wiley & Sons, 1982
Buku Teks
Kumar, Krishan, author
Blackwell, 1996
Buku Teks
National Study Service , 1963
Buku Teks
Castles, Francis G.
Allen & Unwin, 1985
Buku Teks