Phythian, B.A.
Hodder & Stoughton, 1980
Buku Teks
Parrot, Martin, author
Cambridge University Press, 2003
Buku Teks
Jepson, R. W.
Longman , 1936
Buku Teks
Azar, Betty Schrampfer, 1941-, author
Prentice Hall Regents, 1989
Buku Referensi
Ehrlich, Eugene, author
McGraw-Hill , 2011
Buku Teks