Ryan, Michael, 1951-
Wiley-Blackwell, 2017
Buku Teks SO
Kettle, Arnold
Hutchinson University Library , 1972
Buku Teks
Holzberg, Niklas
Routledge, 1995
Buku Teks
MacKay, Marina, 1975-
Cambridge University Press, 2011
eBooks
Kettle, Arnold
Hutchinson & CO (Publisher) LTD, 1967
Buku Teks