Fellin, Phillip, author
Thomson, 2001
Buku Teks
Cohen, Nathan Edward, author
National Ass. of Workker, 1964
Buku Teks
Anderson, David
Macmillan, 1982
Buku Teks
Loewenberg, Frank
F.E. Peacock Publishers, Inc, 1988
Buku Teks
Friedlander, Walter A., author
Prentice Hall of India, 1982
Buku Teks