Weeks, Jeffrey
Longman, 1994
Buku Teks
Benns, Lee F.
Appleton-Century-Crofts, 1955
Buku Teks
Hayes, Carlton J.
Macmillan, 1956
Buku Teks
Stromberg, Roland D.
Appleton-Century-Crofts, 1968
Buku Teks
Smith, Bonnie G.
D.C. Heath and Co. , 1989
Buku Teks