Hunt, Elgin F., author
Macmillan, 1984
Buku Teks
Feather, John, author
Facet Publishing, 2004
Buku Teks
Hunt, Elgin F., author
Macmillan, 1961
Buku Teks
Routledge & Kegan Paul LTD, 1962
Buku Teks
Barnes, Harry Elmer, author
Prentice-Hall, 1950
Buku Teks