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Astigmatism is the most common vision problem. It may accompany nearsightedness or farsightedness. It is usually caused by an irregularly shaped cornea, but sometimes it is the result of an irregularly shaped lens. Either type can be corrected by eyeglasses, contact lenses, or refractive surgery.
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Normal urine is sterile. It contains fluids, salts, and waste products. It is free of bacteria, viruses, and fungi.
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There are 20 feet of blood vessels in each square inch of human skin.
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Cyanide works by making the human body unable to use oxygen.
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Bacteria have flourished on the earth for over three billion years. They were the first life forms on the planet.