Porter, Lindsay
Porter Publishing, 1995
Buku Referensi
Ang, Tom
Mitchell Beazley, 1999
Buku Referensi
Drago, Carl
Blackwell Publishing, 2007
Buku Referensi
Ziegler, Kathleen
Rockport Publishers, 1994
Buku Referensi
Drago, Carl
Blackwell, 2014
Buku Teks