Collier's encyclopedia : volume 1
Macmillan Educational Company, 1990
 Buku Referensi
Collier's encyclopedia : volume 2
Macmillan Educational Company, 1990
 Buku Referensi
Collier's encyclopedia : volume 3
Macmillan Educational Company, 1990
 Buku Referensi
Collier's encyclopedia : volume 4
Macmillan Educational Company, 1990
 Buku Referensi
Collier's encyclopedia : volume 5
Macmillan Educational Company, 1990
 Buku Referensi