The Association for Supervision and Curriculum Development, 1978
Buku Teks
Watson, Richard A., author
Harcourt, Brace and World, 1969
Buku Teks
United Nations, 1977
Buku Teks
The Cedar Press, 1978
Buku Teks
Robertson, Arthur Henry, 1913-, author
Manchester University Press, 1992
Buku Teks