Williams, Glanville
Stevens & Sons, 1963
Buku Teks
Watt, Gary, author
Blackstone Press Limited, 1998
Buku Referensi
Rodgers, M.E., author
Blackstone Press Limited, 1998
Buku Referensi
Barnes, A. James, author
Richard D. Irwin , 1978
Buku Teks
Esther, author
Hay House, INC, 2008
Buku Teks