Geddes & Grosset, 2003
Buku Referensi
Bolander, Donald O., author
Lexicon Publication, 1993
Buku Referensi
Tireman, L.S.
The University , Iowa City, 1930
Buku Klasik
Fergus, Patricia M., author
McGraw-Hill, 1991
Buku Teks
Frank, Marcella, author
Prentice-Hall, 1972
Buku Teks