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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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Multiple experimental evidences have confirmed that at the molecular level, cancer is caused by lesions in cellular DNA.

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There are over 65,000 known species of protozoa. About 10,000 species are parasitic.

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The Romans did not use numerals to indicate fractions but instead used words to indicate parts of a whole.

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The average human gut is home to perhaps 500 to 1,000 different species of bacteria.

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