Myers, Gustavus
Random House, 1943
Buku Teks
Risjord, Norman K.
Prentice-Hall, 1985
Buku Teks SO
Alden, John Richard
American Book Company, 1960
Buku Teks SO
Kemmerer, Donald L.
Littlefield, Adams, 1956
Buku Teks SO
Williams, T. Harry
Alfred A. Knopf, 1963
Buku Teks SO