Williams, John, author
Mainstream, 2011
Buku Teks
Murray, Peter, author
Murray, 2014
Buku Referensi
Craven, Paul R., author
Dickenson Publishing, 1968
Buku Teks
Bennett, A. Gordon
Gloucester, Mass, 1980
Buku Teks
Griffith University,
Majalah, Jurnal, Buletin