Cook, Vivian, author
ARNOLD, 2001
Buku Teks
Ellis, Rob, author
Blackwell, 1990
Buku Teks
Richards, Jack C., author
Cambridge University Press, 2015
Buku Teks
Leaver, Betty Lou, author
Cambridge Press , 2005
Buku Teks
edited by Carol A. Chapelle and Shannon Sauro
Wiley Blackwell, 2017
Buku Teks