Collins, Janet, author
Routledge, 1997
Buku Teks
Brown, Douglas, author
Pearson Longman, 2007
Buku Teks
O`Shea, Tim, author
Harvester Press, 1983
Buku Teks
Timmins, Geoff, author
Sage, 2006
Buku Teks
by George E. Miller ... [et al.]
Harvard University Press, 1968
Buku Teks