(1981). The 1981 world book year book.: The annual supplement to the world book encyclopedia (ed.). World book- childcraft international, Inc..

The 1981 World Book Year Book.: The Annual Supplement to the World Book Encyclopedia. ed. Chicago: World book- childcraft international, Inc., 1981.

The 1981 World Book Year Book.: The Annual Supplement to the World Book Encyclopedia. ed. World book- childcraft international, Inc., 1981.