Bridson, Gavin D.R.
Gerland Publishing, Inc., 1994
Buku Teks
Hurt, R. Douglas, author
Garland Publishing, 1994
Buku Referensi
Kemp, Herman C., author
KITLV Press, 1990
Buku Referensi
Vanessa Bainbridge ... [et al.]
International Institute for Environment and Development, 2000
Buku Teks
Groenendael, Victoria M. Clara van, author
Foris Publications, 1987
Buku Referensi