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About 3% of all pregnant women will give birth to twins, which is an increase in rate of nearly 60% since the early 1980s.
The Romans did not use numerals to indicate fractions but instead used words to indicate parts of a whole.
Adult head lice are gray, about ? inch long, and often have a tiny dot on their backs. A female can lay between 50 and 150 eggs within the several weeks that she is alive. They feed on human blood.
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
Thyroid conditions cause a higher risk of fibromyalgia and chronic fatigue syndrome.