Williams, Edwin B., author
D.C. Health, 1926
Buku Teks
Gibaldi, Joseph, author
The Modern Language Association, 2003
Buku Teks
Maimon, Elaine P., author
McGraw-Hill , 2003
Buku Referensi
Fisher, Andrew, 1941-, author
Population Council, 2002
Buku Teks
edited by W.A. Paton
Ronald Press, 1955
Buku Teks