Não informado. (1988). 21st. Century science & technology. 21st. Century Science Associates.
Chicago-referens (17:e uppl.)Não informado. 21st. Century Science & Technology. Washington: 21st. Century Science Associates, 1988.
MLA-referens (8:e uppl.)Não informado. 21st. Century Science & Technology. 21st. Century Science Associates, 1988.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.