Graber, Mark A., author
Oxford University Press, 2015
Buku Teks
Friedrich, Carl J., author
Boston University Press, 1967
Buku Teks
May, James R, author
Cambridge University Press, 2014
eBooks
Oxford University Press, 1995
Buku Teks
Schulz, Ernest B
[publisher not identified], 1956
Buku Teks