Williams, Howard
St.Maitin's Press, 1996
Buku Teks SO
Schippers, Birgit, author
Routledge, 2014
Buku Teks SO
Buzan, Barry
Cambridge University Press , 2015
Buku Teks
Sheldon Anderson ... [and others]
Westview Press, 2015
Buku Teks SO
Berridge, G. R
Palgrave Macmillan, 2015
Buku Teks