Thomas, David A. Lloyd
Routledge, 1995
Buku Teks
Collin, P. H., author
Peter Collin Publishing, 1997
Buku Referensi
Roelofs, H. Mark
The Dorsey press, 1968
Buku Teks
Locke, John, author
E.P. Dutton, 1953
Buku Teks
Reinsch, Paul S.
Commercial Press, 1921
Buku Teks