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In the United States, there is a birth every 8 seconds, according to the U.S. Census Bureau's Population Clock.
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.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
According to the National Institute of Environmental Health Sciences, lung disease is the third leading killer in the United States, responsible for one in seven deaths. It is the leading cause of death among infants under the age of one year.
When blood is deoxygenated and flowing back to the heart through the veins, it is dark reddish-blue in color. Blood in the arteries that is oxygenated and flowing out to the body is bright red. Whereas arterial blood comes out in spurts, venous blood flows.