Leaver, Betty Lou, author
Cambridge Press , 2005
Buku Teks
Larsen-Freeman, Diane
Longman , 1992
Buku Teks
Mitchell, Rosamond, author
Arnold, 1998
Buku Teks
Hummel, Kirsten M., author
Wiley Balckwell, 2014
Buku Teks
Williams, Jessica, edited, VanPetten, Bill, edited
NY : Routledge, 2015
Buku Teks