Greenberg, Edward S., author
Pearson/Longman, 2005
Buku Teks
Porter, Charles O. (Charles Orlando), 1919-2006, author
Macmillan, 1961
Buku Teks
Arblaster, Anthony, author
Open University Press, 1987
Buku Teks
Oxford University Press, 1995
Buku Teks
Schulz, Ernest B
[publisher not identified], 1956
Buku Teks