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Although puberty usually occurs in the early teenage years, the world's youngest parents were two Chinese children who had their first baby when they were 8 and 9 years of age.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
During the twentieth century, a variant of the metric system was used in Russia and France in which the base unit of mass was the tonne. Instead of kilograms, this system used millitonnes (mt).
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
Certain rare plants containing cyanide include apricot pits and a type of potato called cassava. Fortunately, only chronic or massive ingestion of any of these plants can lead to serious poisoning.