Ingham, Barbara
Bershire SLB 2 QL, England McGraw-Hill 1995,
Buku Teks
Power, Jonathan
Longman, 1971
Buku Teks
Wootton, Barbara
George Allen and Unwin, 1938
Buku Teks
Enke, Stephen, author
Prentice-Hall, 1973
Buku Teks
McPake, Barbara, author
Routledge , 2003
Buku Teks