edited by Robert A. Goldwin
Rand McNally, 1963
Buku Teks
Ferguson, John H., author
McGraw-Hill, 1981
Buku Teks
Ferguson, John H., author
McGraw-Hill, 1961
Buku Teks
Patrick, John
Macmillan Publishing Company, 1984
Buku Teks
Todd, Lewis Paul, author
Harcourt, Brace & World, 1961
Buku Teks