May & Baker Ltd., [date of publication not identified]
Buku Referensi
Saunders Elsevier, 2007
Buku Teks
The Reader's Digest Association, Inc, 1998
Buku Teks
edited by Richard J. Wagman
J.G. Ferguson Publishing, 1992
Buku Referensi
edited by Richard J. Wagman
J.G. Ferguson Publishing, 1992
Buku Referensi