edited by Michael Byram
Routledge, 2000 ; 2004
Buku Referensi
Donald Freeman and Jack C. Richardsand
Cambridge Cambridge University Press 1996
Buku Teks
Brown, Douglas
Pearson Longman, 2007
Buku Teks
Cook, Vivian
ARNOLD, 2001
Buku Teks
Fries, Charles Carpenter
University of Michigan Press, 1951
Buku Teks SO