Roberts, Chris, 1959-, author
Carlton Books, 2014
Buku Referensi
King, J. E. (John Edward)
St. Martin's Press, 1990
Buku Teks
King, S.F.
Hart-Orvis Eeducational , 1976
Buku Teks
King, Chris
Longman, 1994
Buku Teks
Salgado, Gamini
Macmillan Education, 1984
Buku Teks