Swan, Michael, author
Longmans Green, 1969
Buku Teks
Dupee, F.W., author
Doubleday, 1956
Buku Teks
Tanner, Tony, author
Profile Books, 1981
Buku Teks
Bulson, Eric, author
Cambridge University Press, 2006
eBooks
Tanner, Tony, author
Longman Group, 1979
Buku Teks