Newby, Julian, 1957-, author
Routledge, 1997
Buku Teks
Abbot, Waldo
McGraw-Hill, 1957
Buku Teks
Compton, Charles, author
McGarw-Hill, 1979
Buku Teks
Downs, Anthony
Little, Brown and Co., 1967
Buku Teks
Gunther, John, 1901-1970, author
Harper & Brothers, 1942
Buku Teks