Farrell, Thomas S.C.
Corwin Press, 2006
Buku Teks SO
Gorman, Alfred H.
Allyn and Bacon, 1969
Buku Teks
Wells, Ronald A.
Mouton, 1973
Buku Teks SO
Parrot, Martin
Cambridge University Press, 2003
Buku Teks
Protherough, Robert
Open University Press, 1991
Buku Teks SO