Keller, Edward A., author
Prentice-Hall, 1996
Buku Teks
Shaw, Beth, author
Springer, 2012
eBooks
Chester, Roy, author
American Management Association, 2008
eBooks
Ballard, Robert D., author
National Geographic Society, 1983
Buku Referensi
Bowler, Sue, author
Erlangga, 2003
Buku Teks