United Nations
United Nations, 1986
Buku Teks
Goldscheider, Calvin, author
Litle Brown, 1971
Buku Teks
edited by D. V. Glass and Roger Revelle
Edward Arnold, 1972
Buku Teks
Matras, Judah
Prentice-Hall, 1977
Buku Teks
Pollard, A.H., author
Bina Aksara, 1982
Buku Teks