Michele M. Betsill, Elisabeth Corell, editor
MIT Press, 2008
Buku Teks
Lakos, Amos, author
Westview Press, 1989
Buku Referensi
Moran, Robert T., author
Gulf, 1991
Buku Teks
Schiavone, Giuseppe, author
Macmillan Reference, 1997
Buku Referensi
West Publishing Company, 1989
Buku Teks