Allen, Harry E.
Macmillan Publishing Company, 1989
Buku Teks
Morgan, Hal
Viking, 1986
Buku Teks
Sky, Alison
New York: McGraw-Hill, 1976
Buku Teks
Rossiter, Clinton, 1917-1970, author
Alfred A. Knopf, 1956
Buku Teks
Bailey, Stephen K., author
Henry Holt, 1957
Buku Teks