Westall, Christopher
Hongkong : Page One Publishing, 2002,
Buku Referensi
Piotrowski, Christine M., author
Wiley, 1999
Buku Teks
Kubba, Sam, author
McGraw-Hill, 2003
Buku Teks
Harmon, Sharon Koomen, author
John Wiley & Sons, 2011
Buku Teks
Studio Vista,, 1975
Buku Teks