Curti, Merle
Harper & Brothers, 1951
Buku Teks
Crawford, William R., author
Frederick A. Praeger, 1961
Buku Teks
Responsive Environments Corporation , 1968
Buku Teks
Commager, Henry Steele, selector
Yale University Press, 1950
Buku Teks
Williamson, Harold F., author
Prentice-Hall, 1951
Buku Teks