Ewald, Helen Rothschild
Prentice Hall International, 1997
Buku Teks
Holt, Rinehart and Winston of Canada, Limited, 1988
Buku Teks
Quible, Zone K.
Prentice Hall International,inc, 1996
Buku Teks
Ewald, Helen Rothschild, author
Prentice-Hall International, 1997
Buku Teks
Bormann, Ernest G., author
Harper & Row, 1965
Buku Teks