Schiller, Bradley R.
Random House of Canada, 1980
Buku Teks
Schiller, Bradley R.
McGraw-Hill , 1997
Buku Teks
Reagan, Michael D.
Oxford University Press, 1963
Buku Teks
American Enterprise Institute, 1985
Buku Teks
Musolf, Lloyd D.
Scott, Foresman and Company, 1965
Buku Teks