De Vries, Mary Ann, author
Macmillan, 1994
Buku Teks
Axelrod, Rise B., author
St. Martin's Press, 1997
Buku Referensi
(hapus1)
McGraw-Hill, 2002
Buku Teks
Mcmahan, Elizabeth
McGraw-Hill, 1984
Buku Teks
Skeat, Walter W., author
The Clarendon Press, 1948
Buku Referensi