Rowland, Diane, author
Cavendish Publishing Limited, 2000
Buku Teks
Rowland, Diane, author
Cavendish Publishing, 2005
Buku Teks
Houndmills Macmillan 1990,
Buku Teks
Harrington, Jon, author
Prentice-Hall, 1991
Buku Teks
Attwood, Gaynor, author
McGraw-Hill, 1989
Buku Referensi