Barker, D. W.
Macmillan and Co., 1953
Buku Teks
French, F. G., author
Oxford University Press, 1947
Buku Teks
Pincas, Anita
Macmillan Press, 1983
Buku Teks
Puchta, Herbert
Cambridge University Press, 2010
Buku Teks
Howard, Godfrey, author
Pan Macmillan Publishers, 1993
Buku Referensi