Coggan, Philip
Penguin Books Ltd, 1989
Buku Teks
Ascher, Kate, author
Penguin Books, 2005
Buku Teks
Osborne, Starr C., author
[American Management Association;, ], 2010
eBooks
Philip Leo
Lembaga Research Kebudayaan Nasional, L.I.P.I., 1975
Buku Teks
Ritter, Lawrence S., author
Basic Books, 1970
Buku Teks