Hewings, Martin
Cambridge University Press, 2005
Buku Teks SO
Hewings, Martin
Cambridge University Press, 2006
Buku Teks
Murphy, Raymond
Cambridge University Press, 1998
Buku Teks SO
Dhanny R. Cyssco
Puspa Swara, 2004
Buku Teks SO
Kaplan, Jeffrey P.
Prentice Hall International, 1995
Buku Teks SO