Gregory, Robert Henry, author
Chatto and Windus, 1963
Buku Teks
Crawford, F. Robert, author
Prentice-Hall, 1973
Buku Teks
Gregory, Robert Henry, author
Wadsworth, 1963
Buku Teks
Orilia, Lawrence S., author
McGraw-Hill, 1982
Buku Teks
Maynard, Jeff, author
Butterworths, 1972
Buku Teks