Dhanny R. Cyssco
Puspa Swara, 2004
Buku Teks
Kaplan, Jeffrey P.
Prentice Hall International, 1995
Buku Teks SO
Makkink, H.J.
Nijgh and Van Ditmar, 1951
Buku Teks SO
Newby, Michael
Cambridge University Press, 1988
Buku Teks SO
Parrot, Martin
Cambridge University Press, 2003
Buku Teks