Artikel Jurnal
Polevoi, Boris
Foreign Languages Publishing, 1949
Buku Teks
Smart, Terry L.
Holt, Reinhart and Winston, 1987
Buku Teks
Alexander, Roy, 1925-
American Management Association;, 2009
eBooks
Evans, G. R. (Gillian Rosemary)
Open University Press, 2002
Buku Teks