A.D. Lopez...[et all]
World Health Organization, 2000
Buku Teks SO
edited by Gary Hoover, Acta Campbell, Patrick J, Spain
The Reference Press, 1991
Buku Referensi
Williams, Neville
Simon & Schuster , 1994
Buku Referensi
World Bank
New York Oxford University Press 1992,
Buku Referensi
Oxford University Press, 1992
Buku Referensi