Skeet, Muriel, author
Churchill Livingstone , 1980
Buku Teks
Nahavandi, Afsaneh, author
Prentice-Hall, 2000
Buku Teks
Oxford University Press, 2005
Buku Teks
Asch, David, author
Crest Publishing House, 1999
Buku Referensi
Speser, Phyllis L., author
John Wiley & Sons, 2006
Buku Teks