Schwartz, David G., author
Idea Group Reference, 2006
Buku Teks
edited by Muriel Albers Bittel, Lester Robert Bittel and Jackson Eugene Ramsey
Grolier International, 1995
Buku Referensi
Beach, Dale S., author
Macmillan, 1980
Buku Teks
Matthies, Leslie H., author
John Wiley & Sons, 1976
Buku Teks
Allen, David, author
Crest Publishing House, 2002
Buku Teks