Cook, Vivian, author
ARNOLD, 2001
Buku Teks
Ellis, Rob, author
Blackwell, 1990
Buku Teks
Larsen-Freeman, Diane
Longman , 1992
Buku Teks
Leaver, Betty Lou, author
Cambridge Press , 2005
Buku Teks
edited by Eric Kellerman and Michael Sharwood Smith
Pergamon, 1986
Buku Teks