Ward, Russel, author
Prentice-Hall, 1965
Buku Teks
Ward, Russel, author
Macmillan, 1987
Buku Teks
Ward, Russel, author
Heinemann educational Australia, 1977
Buku Teks
Crawford, R. M.
Hutchinson's University Library, 1955
Buku Teks
Crawford, R.M., author
Hutchinson University Library, 1952.
Buku Teks