Dhanny R. Cyssco
Puspa Swara, 2004
Buku Teks
Kaplan, Jeffrey P.
Prentice Hall International, 1995
Buku Teks
Makkink, H.J.
Nijgh and Van Ditmar, 1951
Buku Teks
Newby, Michael
Cambridge University Press, 1988
Buku Teks
Greenbaum, Sidney
Longman , 1990
Buku Teks