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

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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.

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The horizontal fraction bar was introduced by the Arabs.

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Ether was used widely for surgeries but became less popular because of its flammability and its tendency to cause vomiting. In England, it was quickly replaced by chloroform, but this agent caused many deaths and lost popularity.

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The B-complex vitamins and vitamin C are not stored in the body and must be replaced each day.

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