Artikel Jurnal
Dörnyei, Zoltán, author
Cambridge University Press, 2014
Buku Teks
Krause, Eugene F.
Prentice-Hall, 1978
Buku Teks
Billstein, Rick, author
Pearson Addison Wesley, 2007
Buku Teks
Musser, Gary L., author
John Wiley & Sons, 2004
Buku Teks