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About one in five American adults and teenagers have had a genital herpes infection—and most of them don't know it. People with genital herpes have at least twice the risk of becoming infected with HIV if exposed to it than those people who do not have genital herpes.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.
Though the United States has largely rejected the metric system, it is used for currency, as in 100 pennies = 1 dollar. Previously, the British currency system was used, with measurements such as 12 pence to the shilling, and 20 shillings to the pound.
The familiar sounds of your heart are made by the heart's valves as they open and close.