The Encyclopedia Americana : volume 21
Americana Corporation, 1964
Buku Referensi
Collier's encyclopedia : volume 21
Macmillan Educational Company, 1990
Buku Referensi
The Encyclopedia Americana : volume 21
Grolier, 1994
Buku Referensi
The World book encyclopedia : volume 21
World Book, 1984
Buku Referensi
The Encyclopedia Americana : the international reference work, volume 21
Americana Corporation, 1960
Buku Referensi