Benns, Lee F.
Appleton-Century-Crofts, 1955
Buku Teks SO
compiled by Jonathan French Scott and Alexander Baltzly
F.S. Crofts & Co., 1930
Buku Teks SO
Stearns, Peter N.
Macmillan, 1967
Buku Teks SO
Stearns, Peter N.
Macmillan, 1967
Buku Teks SO
Hayes, Carlton J.
Macmillan, 1956
Buku Teks SO