Blades, Derek W., author
Development Centre of the Organisation for Economic Co-operation and Development, 1974
Buku Teks
Vandermeulen, Alice John, 1918-, author
Prentice-Hall, 1956
Buku Teks
by United Nation
United Nations, 1991
Buku Teks
Mayo, Diane, author
[American Library association;American Library association, American Library association], 2005
eBooks
Allen, R.G.D., author
Macmillan, 1980
Buku Teks