New York : United Nations, 1968,
Buku Referensi
Departement of Public Information - United Nations, 1956
Buku Teks
edited by Gesina H.J. van der Molen, Willem Petrus Josef Pompe, J.H.W. Verzyl
Nederlandse Studentenvereniging, 1956
Buku Teks
UNESCO, 1951
Buku Teks
Coyle, David Cushman, 1887-1969, author
The New Americanan Library, 1962
Buku Teks