The World Bank, 2008
Buku Teks
edited by Thomas A. Sebeok
Mouton, 1971
Buku Referensi
Esacove, Anne, author
Oxford University Press, 2016
eBooks
Mertz, Henriette
Ballantine Books, 1972
Buku Teks
UK Department for International Development and the Natural Environment Research Council, 2015
Majalah, Jurnal, Buletin