Starratt, Edith E.
Prentice-Hall, 1966
Buku Teks
U.S. Goverment, 2003
Buku Teks
Sayre, Wallace S., author
Barnes & Noble, 1964
Buku Teks
Posey, Rollin Bennett, author
Littlefield, Adam, 1958
Buku Teks
Ferguson, John H., author
McGraw-Hill, 1947
Buku Teks