Downes, William, author
Cambridge University Press, 2003
eBooks
Montgomery, Martin, author
Routledge, Taylor & Francis Group, 2008
Buku Teks
edited by Sohn Ho-min
University of Hawaii, 2006
Buku Teks
Montgomery, Martin, author
Routledge , 1996
Buku Teks
Ruqaiya Hasan, author
Equinox, 2005
Buku Teks