Kellett, Mary, author
Paul Chapman Publishing, 2005
Buku Teks
Hallermann, Sara, author
Buck Institute for Education, 2016
Buku Teks
Richman, Larry, author
[American Management Association, ], 2002
eBooks
Sartika Kurniali, author
PT Gramedia, 2009
Buku Teks
Drago, Carl, author
Blackwell Publishing, 2007
Buku Referensi