Diggs, Steve
Golden Books Centre, 1990
Buku Teks
Aitchison, Jim, author
Prentice-Hall, 1999
Buku Teks
Aitchison, Jim, author
Prentice-Hall, 1999
Buku Teks
Bly, Robert W
Prentince Hall, 1993
Buku Teks
Stansfield, Richard H., author
The Dartnell Corporation, 1985
Buku Teks