Dowling, Barbara Tolley
Newbury House Publishers , 1982
Buku Teks
Voiles, Price R., author
Glencoe, 1993
Buku Teks
French, F. G., author
Oxford University Press, 1947
Buku Teks
Thornley, G. C.
Longman Group Limited, 1970
Buku Teks
Graver, B.D.
Walton Street , 1987
Buku Teks