Hargreaves, Martin
Longman, 1996
Buku Teks
Martin lambert, Michael Leonard, Andrew Metcalfe
Taylor and Francis, 2009
Buku Teks
Franks, Roger G.E.
John Wiley & Sons, 1972
Buku Teks
Mosley, William Henry
Macmillan, 1984
Buku Teks
Williams, Alan
Kaplan Education, 2005
Buku Teks