Machi, Lawrence A., author
Sage, 2016
Buku Teks
MacGregor, Sandy, author
Hikmah, 2007
Buku Teks
Onwuegbuzie, Anthony, author
SAGE, 2016
Buku Teks
Breithaupt, Tim, author
[American Management Association, ], 2003
eBooks
Ziglar, Zig, author
Heinemann Asia, 1995
Buku Teks