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There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
Pope Sylvester II tried to introduce Arabic numbers into Europe between the years 999 and 1003, but their use did not catch on for a few more centuries, and Roman numerals continued to be the primary number system.
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.
Asthma occurs in one in 11 children and in one in 12 adults. African Americans and Latinos have a higher risk for developing asthma than other groups.
Asthma is the most common chronic childhood disease in the world. Most children who develop asthma have symptoms before they are 5 years old.
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