Protherough, Robert
Open University Press, 1991
Buku Teks
Parrot, Martin, author
Cambridge University Press, 2003
Buku Teks
Thornburn, Scott, 1950-, author
Cambridge University Press, 2017
Buku Teks
Gorlewski, Julie A.
Sense, 2012
eBooks
Farrell, Thomas S. C., author
Corwin Press, 2006
Buku Teks