Panjaitan, Merphin, author
Jala Permata Aksara, 2016
Buku Teks
Roskin, Michael G., author
Pearson/Prentice Hall, 2004
Buku Teks
Huntington, Samuel P., author
Simon & Schuster, 2005
Buku Teks
Tickner, J. Ann, author
Oxford, 2014
Buku Teks
Itzkoff, Seymour W.
Peter Lang, 1991
Buku Teks