Extra, Guus, author
Swets and Zeitlinger, 1993
Buku Teks
Cambridge University Press, 2010
eBooks
Woo, Joseph Yam Ting, author
Qesosa Education Publication, 2004
Buku Teks
Stevick, Earl W.
Cambridge University Press, 1982
Buku Teks
Prentice-Hall, 1972
Buku Teks