Singh, U.K., author
New Delhi : Anmol Publications, 1998,
Buku Referensi
edited by Muriel Albers Bittel, Lester Robert Bittel and Jackson Eugene Ramsey
Grolier International, 1995
Buku Referensi
Madura, Jeff, author
Thomson South-Western, 2003
Buku Teks
Allen, David, author
Crest Publishing House, 2002
Buku Teks
Madura, Jeff, author
South-Western College, 1998
Buku Teks