Gultom, Samuel, author
Greenwood Press, 1987
Buku Referensi
United State Information Agency, 1994
Buku Teks
Crawford, Bartholow V.
Barnes & Noble, Inc., 1953
Buku Teks
Otis, William Bradley, author
Barnes & Noble, 1939
Koleksi Publik
Needleman, Morris H., author
Barnes & Noble, 1939
Koleksi Publik