Lyons, John
Cambridge University Press, 1991
eBooks
Greenbaum, Sidney
Longman , 1990
Buku Teks SO
Parrot, Martin
Cambridge University Press, 2003
Buku Teks
Krulee, Gilbert K.
Prentice-Hall, 1991
Buku Teks SO
Keegel, John C.
Regents Publishing, 1976
Buku Teks SO