Thompson, 2003
Buku Teks
Brown, Esther Lucile, author
Russell Sage Foundation, 1948
Buku Teks
Muir, William K., author
University of Chicago Press, 1973
Buku Teks
Ray, Colin, author
UNESCO, 1979
Buku Teks
Powell, Robert, author
Akimedia, 2001
Buku Teks