Stearns, Peter N., author
Macmillan, 1967
Buku Teks
Benns, Lee F., author
Appleton-Century-Crofts, 1955
Buku Teks
compiled by Jonathan French Scott and Alexander Baltzly
F.S. Crofts & Co., 1930
Buku Teks
Weeks, Jeffrey
Longman, 1994
Buku Teks
Smith, Bonnie G., author
D.C. Heath, 1989
Buku Teks