Crystal, David, 1941-, author
Longman, 1993
Buku Teks
Peters, Pam, author
Cambridge University Press, 1995
Buku Referensi
Hughes, Rebecca, author
Routledge, 1996
Buku Teks
Leech, Geoffrey N., 1936-, author
Longman, 1994
Buku Teks
Fayetteville : University of Arkansas
Majalah, Jurnal, Buletin